How bloodline inheritance works, how to breed bloodlines into your dynasty, how to get people with desirable bloodlines into your court and dynasty, how to maximize breeding speed and efficiency, and the potential benefits and downsides of various bloodlines.
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Bloodlines can be either patrilineal or matrilineal, meaning that they are inherited from the father or the mother. A patrilineal bloodline won't be inherited from the mother, and vice versa. This applies to regular marriage, children of concubines/consorts, and known births outside marriage (known bastards).
However, this inheritance restriction is overridden by what is called "matrilineal transfer." This means that in matrilineal marriages, all bloodlines are inherited from both the father and mother, regardless of patrilineal or matrilineal inheritance. This is the key to breeding bloodlines into your dynasty. It currently works for all bloodlines, historical or created, except the Phalaris bloodline and the male Matilde bloodline. The Phalaris bloodline is very rare and exceptionally difficult to create and has better alternatives anyway. The male Matilde bloodline is also very rare, and does not grant major benefits.
(There is also the rare case of extramarital births with an unknown father. These children will receive all bloodlines from their mother regardless of inheritance, but none from their father. Note that his only applies to children who have an unknown father at the moment of birth, and not to denounced bastards, who will receive bloodlines under the usual mechanics per the first paragraph of this section above.)
In order to get bloodlines into your dynasty, you need to take advantage of matrilineal transfer. You do this by matrilineally marrying a male who has a bloodline to a woman of your dynasty. By doing this any children born of that marriage will be of your dynasty, and have any bloodlines either parent has.
Your ruler (or his heir) can then marry the woman of your dynasty with the bloodline(s) matrilineally. Since the woman is of your dynasty the children of the marriage will be as well, and not cause a "wrong dynasty" issue. They will have the mother's culture and religion, though, so if they differ from yours you need to be aware of this and educate the children accordingly.
You will, on occasion, find that there are few or no eligible males of a bloodline to matrilineally wed to women of your dynasty. In this case you can use women to prepare for the next generation. Simply wed women with the desired bloodline matrilineally to highly fertile men. Look for Lustful, or higher-level Stewardship or Diplomacy educations. Avoid marrying them to Chaste or Homosexual men, as those traits reduce fertility. So do Learning education, but by a small amount. Membership in a monastic order has a significant fertility malus for both men and women.
You can find out if someone is a monastic member by hovering over their portrait and watching for the "Is a Member of [society]" message. Monastic members should generally be avoided for breeding purposes. Non-monastic societies like the Hermetics cause no fertility issues.
Since your focus here is to produce the maximum number of children, and not to produce good heirs for yourself, congenital traits are not important (except that Strong gives a fertility bonus). Better to save genetically good spouses for your own dynasty members.
Any children of these marriages will be born with the mother's bloodline(s) since they are matrilineal. Any sons produced can be wed matrilineally to women of your dynasty, to breed the bloodline into it. The daughters can be wed matrilineally to ensure you have backup children born into the next generation in case you have bad luck with the sons.
Note that, as it tends to go in CK2, "stuff happens." If you have only one person with the bloodline in your court, you might find out that that person is infertile, or all their children die young, or the person dies from a disease before they have a chance to breed. Because of this it's better to get as many people with the bloodline as possible into your court, where you can ensure good and fertile marriages, and control of the resulting children.
Some bloodlines have restrictions in terms of religion and will offer no bonus if the character is not the correct religion. The bloodline will still exist on the character and can be passed on normally, but it will have no effect.
Other bloodlines are what I call "semi-restricted." They are active and offer bonuses regardless of religion, but a specific feature is restricted by religion. An example is the Carolingian Blood, which offers a small prestige and personal combat skill bonus to all bearers but has a random event of receiving a great warrior which only triggers for Catholics. The bloodline descriptions make this clear when it applies.
Page 16 of your ledger has a list of all the bloodlines in the current game, extinct or not, along with the number of living bearers of each. Hovering over them will give you a description of their effects. Clicking them will bring up the founder's character screen. There you can click his bloodline button (the red drop of blood) which will bring up a screen with a list of his bloodlines. Usually it's only the one they founded. In this new screen you can then click the red drop of blood (identical to the one in the previous screen) next to the portrait by that bloodline to get a list of the still living bearers of that bloodline.
Some bloodlines do not allow bastard inheritance. This means that while all the normal mechanics (like matrilineal transfer) are in effect, a bastard-born child cannot inherit the bloodline through any method, ever. These kinds of bloodlines are thankfully rare. To my knowledge the only ones that do not allow bastard inheritance are the Matilde bloodlines, the blood of Phalaris, and the saintly bloodlines. Note that the pagan equivalent of saintly bloodlines, ancestor veneration bloodlines, DO allow bastard inheritance.
Well, those are the basics of bloodline breeding. You now know everything you need to breed basically any bloodline in the game into your dynasty. In the rest of this guide I will cover strategies to supercharge the breeding to ensure quick and efficient bloodline reproduction and integration, bloodline creation and timing, bloodlines that are double-edged swords, acquiring good breeding subjects, and of course, incest. Has any CK2 topic ever been broached without incest coming up?
You will find that most of the guide is male-centric. This is partly because most rulers are male due to game mechanics, and partly because mass-breeding (covered below) requires one to be male for biological reasons. I do include a section on what to do as a female ruler.
Your Best Breeding Buddy: The Seduction Focus
This section is the most important part in supercharging your breeding success. It requires the Way of Life DLC. If you don't have this DLC, you can safely skip this section. I would recommend that you get it, though. Regardless of bloodline breeding, it's the DLC that adds the most fun and variation to the game in my opinion.
To truly ensure that you maximize the number of candidates with bloodlines to wed into your dynasty, you need to help the women on the way. Even if you wed women to fertile men, sometimes the luck of the draw will leave them childless or all their children dead. Or perhaps a woman of your dynasty is wed to a man with a bloodline, but he's just not doing his marital duty. Enter you. Or the reverse, rather. Well, you know...
To help nature on its course we are going to engage in mass-breeding. I assume that you have a basic knowledge on how to select a focus, and how to use the Seduce decision of the Seduction focus. If not, consult the Wiki or a guide on the topic.
While the basic function of the Seduction focus is simple, there are many things in it that are never explained in-game, yet have a profound effect on its success. One is what levelling does. When you succeed in the Seduction focus you have a chance to level your seduction ability, level your Intrigue education trait if you have one at level 1-3, or become a court tomcat.
Seduction levelling starts with Aspiring Seducer which gives +15 attraction opinion. The next step is Seducer which gives +1 Intrigue and +30 attraction opinion. The third level sees the modifiers replaced by a lifestyle trait, Master Seducer, which ups the attraction opinion to +50, and also gives an almost foolproof seduction method option in the final step of seduction. At this point you can choose to take this Master Seducer trait (which replaces the Seducer modifier), take the Hedonist trait, or decline both lifestyle traits and just keep going with the Seducer modifier and the ability to acquire another lifestyle trait. Note that if you decline the lifestyle trait you will never get the chance again with this character, so make sure you make the right choice.
Most of this is explained in-game. What is not explained in-game is that even the first two modifiers increase your chances of seduction success, so you want to level as quickly as possible if you are going to be seducing. If you are willing to go to Master Seducer that will be enormously helpful. If you have your mind set on another lifestyle trait, then simply level to Seducer and decline the lifestyle trait if the option pops up. Never pick Hedonist for bloodline breeding purposes. It is not helpful. It does not give the magic seduction ability of Master Seducer and the fertility bonus only affects your chance to randomly impregnate your wife and possible lovers, not your use of the Seduction focus.
There is also a modifier called Court tomcat which gives +1 Intrigue and a +10 attraction opinion. What is not explained in-game about this modifier is that it vastly increases your chance of keeping your bastards secret. Some options for suspicious husbands (like laying traps for the wife's bull) cannot be used at all against court tomcats, and the risk of being suspected and/or discovered is greatly reduced regardless of what action the husband takes.
As a concrete example of just one effect of Court tomcat, the chance of a husband investigating a child's paternity finding nothing is multiplied by five (!) if you have court tomcat. As a comparison, Master Seducer multiples the chance of no finding by 1.5, and the Master Schemer Intrigue lifestyle trait doubles the chance of no findings. The Seduction and Intrigue levelled modifiers have no effect on this particular event (though they do on other adultery events). There are also random events triggering suspicions in husbands that cannot fire at all if you have Court tomcat. For large-scale siring of secret bastards Court tomcat is your best friend.
To level seduction, it is best to invite a Lustful woman to your court. They will almost never reject you when they have a good opinion of you if you use the lewd suggestion option at the final stage of seduction. Then simply move time forward a day and seduce them again. Ideally pick a woman of age 45 or higher so she can't get pregnant and your court doesn't get cluttered with useless bastards. Make sure she does not have the Great Pox. Repeat until you have Master Seducer (or the Seducer modifier if you are not taking the lifestyle trait) and court tomcat.
Court tomcat has only a 1/20 chance of being awarded with each successful seduction, but as explained above it is vital for successful large-scale breeding. The modifiers are easier to acquire: a 1/2 chance of getting Aspiring Seducer, 1/5 chance to get Seducer, and 1/10 chance to get the lifestyle strait. Since this progression is a levelling one, unlike Court tomcat, you cannot get Seducer until you have Aspiring Seducer, and you cannot get Master Seducer/Hedonist until you have Seducer. Because of the separate processes you will on occasion get Court tomcat before you even get Aspiring Seducer (very rare, though it has happened to me more than once), or you may be a Master Seducer and still not have Court tomcat 50 seductions later. That's just life with a random number generator.
(By comparison, if you have an Intrigue education, the chances of levelling from level 1->2 is 1/10, 2->3 is 1/20, and 3->4 is 1/100 (!). Just through the regular process of acquiring the modifiers for breeding you are likely to level at least once, but reaching level 4 is a bit unlikely. Note that these odds are the same as the chance of levelling on successful spying with the Intrigue focus, but Seduction successes happen more often with good modifiers, so the Seduction focus is actually a more efficient though more click-intensive way of levelling Intrigue education than the Intrigue focus is!)
The woman's opinion of you also influences the chance of success. The bonus tops out at opinion +60 or opinion +75, depending on the particular seduction event is triggered for the woman.
What you are going to do is impregnate women who have the bloodline (or who are matrilineally married to men who have the bloodline) you are trying to breed, to make sure plenty of children are born with the bloodline and can be used as breeding stock later on. It is vital that they are in a matrilineal marriage. The key is that everyone else in the world thinks that they truly are the children of the spouses, in order for the bloodlines to pass on to the child. If the affair is discovered and the child labelled a bastard, no bloodlines will be inherited from the mother or the spouse (unless the mother happens to have a matrilineal bloodline, which is highly unlikely).
Another thing that is not explained clearly in-game is that each time you successfully seduce a woman, you have a chance of making her pregnant. For this reason, when you get the option to leave them ("Veni, Vidi, Vici") or make them your lover, leave them. You don't want to make them your lover, because while this gives a chance of random pregnancies, you cannot seduce your lover or ex-lover. By making them your lover you block yourself from ever seducing them again. And you will be seducing the same women over and over again.
It takes a couple of months for pregnancies to show up in-game, so you won't know if they are pregnant right away. Seduce another woman in your court that is ready to pass on bloodlines. Repeat, repeat, repeat. If you have a few promising women in your court, you will have more than enough to keep yourself busy. You will rapidly have a court full of squalling children with lovely bloodlines flowing through their veins.
The chance of pregnancy after seduction varies by fertility. For a woman to get pregnant at all she has to be under 45, she has to have at least 20% fertility, and you have to have at least 20% fertility. Since the default fertility is 50%, it is very rare to fall under 20% unless there are at least three major fertility debuffs.
You don't generally have to worry about your own fertility. Even if it is too low, every successful seduction there is a 15% chance of losing Chaste if you have it, and gaining Lustful if you don't have it. Getting rid of Chaste increases your fertility by 15%, and gaining Lustful increases it by +20%. You will almost certainly be above 20% fertility, and increasing your fertility beyond that point will not increase the chance of impregnation.
The chance of impregnation is based on the woman's fertility ranges from 1/20 (at fertility 20-33%) to 1/2 (fertility 60% or above). The impregnation chance at average fertility, 50%, is approximately 1/3. Here you can clearly see the importance of traits for wives who are bred with bloodline-bearing men. Being Chaste alone will bring the average woman's impregnation chance from 33% to 15%, i.e. reduce it by more than half. On the other hand, if she's Lustful it goes from 33% to 50%. This makes it very easy to breed with them. I've wed Lustful women to husbands with bloodlines and bred them until they quite literally died from all the childbirths. At which point I immediately wed the husband to another woman.
(I would only recommend going this far to save bloodlines that are at risk of extinction. Playing with the Seduction focus for 15 years is not that much fun nor very good for character development.)
When picking husbands for women with bloodlines, you can be less picky about their fertility traits when you use the Seduction focus to breed the women. Be more focused on the husbands having low Intrigue, which will decrease their chances of discovering that the child is a bastard. The lower the better since each bastard discovered is a wasted child, not to mention the wasted time on seduction and 9 months of pregnancy.
In addition to the father finding out that the wife's child is not his, you can also be caught in the affair itself. High Intrigue characters in your court can catch you, with an especially high risk of relatives catching you. Whither family solidarity!?
Sometimes they will just tell everyone, granting you and your fellow cheater the Adulterer and Adulteress modifiers for 10 years. It's a -5 general opinion modifier and an additional -5 church opinion modifier. Unpleasant, but not a big deal.
(Women get double the penalties, -10/-10, because sexism.)
Be careful about incestuous adultery, though, as this gives the Incestuous adulterer/adulteress which has double the penalties, -10/-10 for men and -20/-20 for women. In addition to this, if you are Catholic you may soon find out the hard way that the Pope is particularly excommunication-happy when it comes to incestuous adulterers. So, leave your aunts and sisters alone, folks!
Occasionally the person catching you will blackmail you. They will keep your secret in return for a bribe. Don't take them up on it. It's usually quite expensive, and only covers that one occasion. Next time you seduce someone the very same person may catch you again, asking for another bribe. Let's say this happens three times and you pay the expensive price each time. The fourth time you get fed up and refuse. They now tell anyone, you get the negative modifiers, and they keep the money from the first three times. Sorry, no refunds!
In addition to this, each time there is the chance of them telling everyone right away without giving you a chance to buy their silence. You may grudgingly have paid five bribes to a person, then they catch you a sixth time, and out you right away without blackmail. You get the modifiers, and as for the first five bribes, guess what... Sorry, no refunds!
Paying bribes may make sense if you only seduce someone once in a blue moon, but for the large-scale breeding we are doing here, you should simply accept that the Adulterer modifier is probably going to be part of your life for the coming 10 years.
Fortunately, while being discovered and labelled an adulterer is fairly common, having the bastardy of children discovered is pretty rare if you are a Court tomcat. Knowing that you cuckolded them makes them more suspicious, but with the modifiers are low Intrigue on the husband you usually still get away with it. I've had husbands who knew I cuckolded their wife five times, say, she bore three of my children, yet the husband still believed all three were his. Go figure.
Finally, there is a chance that a woman being seduced gives a "hard" rejection, which prevents you from trying again. It's pretty rare, and the chance is reduced by the seduction modifiers, but with the amount of seduction you will be doing you're bound to run into it sooner or later. It lasts for five years, after which you are free to try again. Just seduce other women in the meantime, or switch focus and come back to her later if necessary.
As I mentioned above, you should avoid wedding your subjects to homosexuals due to the reduced fertility. If your bloodline bearer is the one who is Homosexual, though, there's nothing you can do about that. If the subject is male it's not much of an issue. Wed him to a fertile woman and impregnate her as usual. His fertility won't matter here.
If it is a female subject, though, you're at a loss. Homosexuals can only be seduced by same-sex homosexuals, which cannot result in children. In this case all you can really do is wed them to a fertile man and hope for the best. Homosexuals can still bear children in marriage, though at a reduced rate. If Homosexual is combined with Chaste and monastic order membership, though, you might want to write that woman off as a loss. She's unlikely to ever become pregnant.
If she's easily invited to or already in your court, sure, wed her and maybe you'll get lucky. But don't put any effort into getting such a subject to your court unless they're the last bearer of a bloodline you really want.
Acquiring Bloodline Subjects
What do you do if you want a bloodline where there isn't a single bearer you can invite to your court, even with gifts?
The first thing to do if you have some extra money is to check if you can use a favor to force them over (requires the Conclave DLC). You can buy a favor from them for a scaling cost depending on their parentage. Make sure you check this cost before you buy the favor: paying 800 gold for a subject is usually not worth it unless it's a truly exceptional bloodline at risk of extinction. The average cost seems to be 80 gold, and the lowest I've seen is 40 gold.
If their opinion of you is not high enough to sell you a favor, it can usually be brought up enough to sell you one by sending them a gift. If you can afford a favor, you can presumably afford the extra 15 gold for the gift. This may not be enough if they truly dislike you (if you are a kinslayer, or wrong religion and they are Zealous, etc.), but it usually is. It's rarely an issue with women since seduction modifiers tend to keep their opinion of you high.
Note that favor-forced invites work without the normal religious restrictions. You can force over Muslims if you are a Christian, etc., without issue.
Forcing a courtier over with a favor requires them to be unmarried, not a close relative of their liege, and not a councillor. Non-councillor positions such as commander or court physician do not block forced favor invites, though.
Another option is raiding. If you are able to raid, you can siege down a holding where there are courtiers who have the appropriate bloodline, and hope you capture one so you can recruit them. If there is a woman you cannot recruit but you are allowed concubines, you can simply make them your concubine and immediately put them aside, which will make them members of your court and free to marry. The opinion malus can be offset by a gift, or through seduction if you have good modifiers for it.
While raiding for subjects is inexact and unreliable, in my experience capturing prisoners is quite common when you successfully siege down a holding. Since AI courts are usually not very large, and there seems to be a good chance of capturing family members of the ruler (who are usually the ones carrying bloodlines), it is a reasonably effective way to acquire subjects if you have the military strength for it.
(Looting is the only way I know of to acquire subjects from outside of your diplomatic range.)
To some extent this process is likely to involve incestuous relationships. You will sire many secret bastards. Since the game doesn't display the true father of children (even if you know it's you!) it can be easy to accidentally do things like wed brother to sister. I accidentally wed my own secret bastard daughter once when my previous wife had lost her usefulness and needed to be replaced, and was rewarded with an uncomfortably high rate of Inbred children.
You also have the fact that when you wed matrilineally within your own dynasty there will _always_ be a family relation, though hopefully a distant one. The game calculates the risk of inbreeding by common ancestors, but only goes five generations back, so after a while marrying distant dynastic relatives can become risk-free.
But what do you do when you're in a situation where you are trying your best to avoid inbreeding yet the odd child still comes out Inbred? Take a break from the hardcore breeding. Wed your children to people where there are no common ancestors at all within the past five generations. Unless your realm and dynasty are enormous, this should be very easy by just marrying someone from another realm. If that is not a good solution for your situation, you can use the invite noble/introduce debutante decisions. They generate new characters so you will have completely fresh genes there to dilute the concentration of family genes (though the new characters are usually not stellar breeding material). A generation or two of this should make quick work of any inbreeding problems.
You can create your own bloodlines in three main ways: through the Forge Bloodlines ambition, through pagan warrior lodges, or through completing certain in-game objectives or events (like becoming the Saoshyant). The ambition is special in that, unlike the others, it is not available to you if you already have a created bloodline in you. Since it allows you to create unique bloodlines not available in any other way, most of them quite useful, I would recommend not creating or breeding a created bloodline into your rulers until you have had a chance to forge one through the ambition.
This ambition becomes available once you have 5,000 prestige. It is also available to children with 2,500 prestige, if they have any of the traits Ambitious, Genius, Proud, Quick, or Willful. Unless you have very high dynasty prestige, you are unlikely to ever have enough prestige as a child.
One caveat is that if anyone in your dynasty has ever forged a bloodline, the prestige requirements are raised to a whopping 20,000 for adults and 15,000 for children. However, the AI is set to never pick the Forge Bloodline ambition if they are of the player's dynasty, so the only way this would happen is if you forged a bloodline and later lost it. An unlikely situation.
Beware of creating bloodlines with a female ruler! Bloodline inheritance is determined by the creator's gender, so male rulers will create patrilineal and female rulers will create matrilineal bloodlines. Since most rulers are male, they cannot pass on matrilineal bloodlines except through matrilineal transfer. This means that they will be limited to matrilineal marriages lest they lose the bloodline and then need 20,000 prestige to forge a new one. Only if you have an enatic succession model should you consider creating matrilineal bloodlines.
Christians, and reformed pagan religions with ancestor veneration doctrine, can also see a dead ancestor become beatified, sainted, and then founding a saintly bloodline (I use the Christian terms here for ease of reading, but please interpret what I am saying as universal). The specific bloodline founded and its effects is picked randomly from a list in the game files, though it can be affected by the traits of the deceased. There is a long list of modifiers that make a character a more likely candidate for sainthood, or that can eliminate him completely from consideration, on top of those who influence what particular bloodline a sainted character creates. That is beyond the scope of this guide, but there are excellent guides on the topic out there, and Google can quickly find them for you, in case you want to aim at having one of your characters sainted.
Do note that saintly bloodlines do not count as created bloodlines for the purposes of forging your own, so they can safely be held and bred into your dynasty without limiting your options (though having a saintly bloodline makes you less likely to be sainted after death yourself). All these bloodlines are restricted to the religion of their founder, and will be inactive for anyone else. Unless you are planning to switch to that religion, they are not worth breeding into your dynasty, especially since they will still reduce your chance of being sainted yourself if you have no other saintly bloodlines.
Most bloodlines are entirely positive. While there are no outright negative bloodlines, some can have positive effects combined with negative ones, and others can have side-effects that while not expressly negative, can still have a negative effect depending on circumstances.
An example of the first type would be the Blood of Baudouin. It has four positive effects: +0.10 monthly prestige, +5 Latin opinion, enables castration, enables blinding. However, it also has one negative effect: -5 Byzantine opinion. Whether this is worth it or not would be up to you. In one game it might be worth it, in another game it might not. At least the negative effects here are clear and easily grasped.
Other bloodlines have more sinister effects, in that they are not clearly visible from the game. Sometimes they are hidden in the game files and cannot even be ascertained in-game.
An example is the Heir to Alexander bloodline. It is a bloodline that is founded through events under certain prerequisites, and is one of the better bloodlines in the game. In addition to various smaller bonuses, it increases levy reinforcement rate and gives its holders a once-per-lifetime full-scale invasion CB. It also gives characters a higher chance of becoming Ambitious. The random Ambitious event is 15 times (!) more likely to fire, the character is guaranteed to get the Ambitious trait rather than just have a % chance based on other traits, and the event will not give the option to become Content. Useful for you and your heirs, less pleasing in a vassal. It also makes sure that when a character loses a random personality trait due to having too many it won't be Ambitious. The trait can still be lost through other events, but it will never be randomly lost, and considering how good the trait is this is very beneficial for a player.
It has a side-effect, though. A person who has an ambition bloodline cannot become the child of destiny. If you have any hope of ever playing a child of destiny (and players have an increased chance of becoming one compared to NPCs), acquiring the Alexander bloodline will eradicate that possibility. The immortality bloodline also eliminates this possibility, as the game disables the child of destiny chance from any character with a bloodline with the ambition mechanic. The Alexander, child of destiny, and immortality bloodlines are the only three bloodlines that have this ambition mechanic.
Another example of a double-edged sword is the murder bloodlines, created through the Forge Bloodline ambition. While the murder bloodlines can be very good (the blood of the dragon is, in my opinion, the most overpowered bloodline in the entire game), they also make AI characters murderous. What this means is that not only does the AI become twice as likely to murder plot, it also becomes very indiscriminate in its targets. Most AI characters only murder for a reason, as bad as the reason may be. NPCs with murder bloodlines become like Lunatic and Possessed characters in selecting murder targets, which means that they might end up murdering someone for no real reason.
Beware: the immortality bloodline also makes the AI murderous. While it is a very useful bloodline since it gives +1 health, imagine all your descendants living longer due to that extra health, being twice as murderous as anyone else, very likely to become Ambitious and very unlikely to ever lose the trait, and being indiscriminately murderous like a Lunatic. Add claims and pretenders on top of that, and I don't think I have to draw you a picture of what can happen with a large dynasty, do I? And if you happen to be Muslim where brothers hate each other and there is no kinslayer malus, oh boy...
Funny enough this is not the result of developer oversight, but of someone who watched too much Highlander. The developers put a comment in the game files by that bloodline:
#Murderous + Ambitious = "There can be only ONE."
Unlocking Specific Features
One fun thing with bloodlines is that in addition to bonuses, many of them allow us access to features we normally wouldn't have access to. I already mentioned a bloodline that allows you to blind and castrate regardless of culture. There are also bloodlines that enable you to perform sky burials, send your children and siblings away to prove themselves in Horse Lords-style mercenary companies (not to be confused with Conclave-style assembled mercenary companies), allow you to duel, allow you to gain the Viking raiding traits (though Viking is renamed Pirate if you are not Germanic), or allow you to use tanistry succession.
These unlocks are always available to anyone who has the correct bloodline active, regardless of religion, culture, government type, focus, etc. Want to play a Swedish Catholic who can duel anyone freely, can castrate and blind their prisoners, and buries their dead with sky burials while choosing their successors through tanistry? No problem, with the right bloodlines!
For further information on what the various bloodlines do and any special features they enable, I refer you to the Wiki. This topic alone could produce a guide twice the size of this one.
Note that almost all bloodlines offer monthly prestige and personal combat skill bonuses. While the bonuses are small, and an individual bloodline will not have a significant impact, over time they can add up. +5 personal combat skill is nice, but not much. Coming out of the womb with +60 personal combat skill is pretty impressive, though! So even if a bloodline does not seem very impressive, if you get the chance to breed it in, why not?
We've all had the situation where we really want a bloodline, only to find out that it has gone extinct, or the only bearer is a 69-year-old woman with cancer. What to do in such a situation?
Cry is what you do. You cry. As far as I know, there is no way to raise the dead in CK2.
This issue has plagued me many times. I cannot count the number of times I have played a 769 starting date as a non-Germanic, only to see Ragnarr Loðbrok die long before his Viking trait-enabling bloodline has spread. Last time he became Chaste and Homosexual and died of the flu at age 26. C'est la vie, or should I say c'est la mort?
Fortunately, unlike Ragnarr Loðbrok's, most bloodline features are available in more than one bloodline. If Muhan Ashina's bloodline has gone extinct, Khan Kubrat of Bulgaria's bloodline offers the same ability to send children and siblings away as mercenaries. There are very few unique bloodline traits among the historical bloodlines, though bloodlines forged through the ambition tend to have them.
The Sayyid Trait
The Sayyid trait is not a bloodline but an old trait that is inherited like a patrilineal bloodline without matrilineal transfer. In other words, it is passed on from father to child without exception, but never from mother to child. Children of Sayyid mothers get the Mirza trait. The Mirza trait is never passed on in any way.
The Sayyid and Mirza traits have two effects: a +5 Muslim opinion bonus and an easier time creating most caliphates. It is not a very useful trait if you are non-Muslim (unless you happen to have lots of Muslim vassals for some reason). Still, it can be fun to get just for the heck of it. In order to pass it on down your line, its patrilineality requires you to have a female ruler marrying a Sayyid man. The trait is pretty prolific, so it's usually not too hard to force a Muslim man over with a favor-invite and wedding him matrilineally to your female ruler. Muslim men tend to marry pretty quickly, so likely you will have more luck among young men. Raiding is also a viable option here just like with bloodlines.
So, you're playing as a female ruler, and most of the breeding strategies above don't apply to you. What do you need to do differently, and are there any special benefits to this situation?
Since you cannot impregnate multiple others but can only be impregnated yourself, the breeding strategy will have to be completely different. You can pass on any bloodlines from your husband and your own (assuming you are matrilineally married, which a ruler always should be), but that's it.
If you want the Sayyid trait, I'd advise you to wed a Sayyid, since female rulers are your only way to breed that trait into your descendants.
Unless you are using an enatic succession form, where you are always a female ruler, I'd advise against creating any new bloodlines. If you do, they will be matrilineal, and fathers won't be able to pass them on except in matrilineal marriages. This means that your male heirs will have to choose between matrilineal marriage or losing the bloodline, which in the end means a choice between inbreeding, game over, or losing the bloodline. Not a nice choice. And since if you had forged this bloodline through the ambition it massively increases the prestige requirement to pick the ambition again, even replacing it with a new one will be much harder. Best not to do it.
What you can do for breeding purposes is get pregnant by men with good congenital traits. Assuming your husband doesn't discover your infidelity, the child will be legitimately his (on paper) but will benefit from the genetic heritage of the true father, yet still carry all the bloodlines of you both. This can be a nice break from being focused on spouses purely for bloodlines and can help correct any "genetic lag" this has caused for your dynasty. It can also help ensure you have plenty of children. This may be your only chance to get Sayyid bred into your dynasty, for example, so you may want many, many sons to ensure that they don't die off and the trait with them. Since each successful seduction gives a chance of pregnancy, as a female ruler you can virtually be almost constantly pregnant, especially since Seduction tends to add the Lustful trait with its +20% fertility bonus.
Be aware that updates with pregnancy events have been added to the game that, unless you change it in the game rules, force you into regency for the final part of pregnancies. There is also a chance of good and bad events in pregnancies, with the risk of bad results increasing with the number of children birthed and the mother's age. The age risk starts at age 27 and keeps growing intermittently until age 50 (though pregnancies stop at age 45, so technically it tops out at age 45 as that is the latest time you can normally give birth), and the risk with number of children starts at 3 children and then increases at 4 and 5. Traits, illnesses, and health can affect the risk positively or negatively. Being under the age of 19 also increases risk. If you've ever had a terrible pregnancy but survived, you will be labelled a "survivor mom" (not visible in-game) and any further pregnancies will have massively increased risk.
Personally, I like to breed my female rulers like crazy with Genius men. With the seduction focus and court vixen (the female version of court tomcat) the husband is usually none the wiser, and if he catches one or two of a dozen children, so what? Plus, if you start early then your first-born son should be adult and ready to rule without regency when birth complications claim you.
If you are more interested in breeding your female ruler, which really is not part of the topic of bloodline breeding, there's a whole ton of guides written on this topic. The Wiki also describes the mechanics of breeding. Note that there is currently a reported bug where non-bastard children only inherit base attributes from their mother, so you are better off focusing on congenital traits than attributes when selecting impregnators.
(Beware that if you plan to live into late age, women lose attraction bonuses at age 45 rather than 65 as men do, so the Master Seductress lifestyle trait is usually not a good choice for long-lived women.)
I once got 14 or 15 children out of my female ruler, I think, before she died of birth complications. Her first-born son was in his 20s and fit and ready to rule, and he had the Sayyid trait which then passed down through my rulers for the rest of that game. It was a fun break from bloodline breeding.
Sometimes you will have a bearer of a bloodline near extinction in another court, and you have no way to get them to your court to breed them. In this case you can seduce them from afar, which will enable you to bring their opinion of you up to +100. Note that distance can increase the time it takes to seduce. You will occasionally get pop ups saying they are very far away. You can click to continue the seduction. You will eventually have the events trigger, but it can take a long time if they are far away.
If they still won't come, you can make them your lover, which makes them more likely to come, and also increases the chance that you will impregnate them randomly. This means you can't seduce them any more, but having a lover with a chance of children is better than an extinct bloodline. Note that this only works for matrilineally married women, so you are usually restricted to seducing faraway rulers here. If they are married normally (patrilineally) the mother will not pass on bloodlines so impregnating them is pointless, and if you are a woman then obviously the child will be yours, so it cannot inherit any bloodlines from the man's wife (but from him, if the bastardy becomes known). If it is a man carrying bloodlines who can't be brought to your court then impregnating his wife can be beneficial as normal, though.
Note that to seduce someone outside your realm they have to be of the same religious group as you, though they don't need to be of the same religion.
In case you are interested in looking at the game files yourself to learn and understand more of the topics discussed in here (highly recommended!), here are the technical names of various things I have discussed:
- Aspiring seducer: wol_seducer_1
- Seducer: wol_seducer_2
- Master Seducer: seducer
- Master Seductress: seductress
- Court tomcat: wol_court_tomcat
- Court vixen: wol_court_vixen
- Hedonist: hedonist
- Chaste: chaste
- Lustful: lustful
- Homosexual: homosexual
- Adulterer: adulterer
- Adulteress: adulteress
- Incestuous adulterer: incestuous_adulterer
- Incestuous adulteress: incestuous_adulteress
- Ambitious bloodlines: bloodline_ambition
- Murderous bloodlines: bloodline_murderous
- Forge Bloodline amb.: obj_forge_bloodline
- "Survivor moms": survivor_mom
You can search the game files for these terms to easily find how and when various things I've mentioned are used and affect you.