This guide tells you the strengths and weaknesses of all the troops in the game. It will also say about how these troops work and good combinations to use in battle.
Thalya is a key troop that will be essential throughout the campaign, whether it's the very high damage output for early in the game, special interactions with objects or the fact that the final level is literaly impossible (to my knowledge) without her.
At the start of every mission, she is level 1 and cannot gain experience EVER. The only way to improve her is by spending evilness and lots of gold to increase her damage and helth, plus give her a new ability (availble from mission 2 so not a spoiler). Her basic attack is ranged and does a lot of damage, particularly early game. Back her up with 2 of each type of normal horde creatures and this will crush through many enemies. She also has 2000 health at level 1
Her special ability unlocked straight from the start is fire bomb. This attack even when not upgraded will take nearly half the health off basic enemies and it deals splash damage that does not drop off from the impact. The only problem is how long it takes to fire and then reach its target. If you aren't careful when using it, the enemies will just move out the radius when they rush to attack your creatures.Also, the AI has an annoying tendancy to not use the power of it properly. It will just fire it directly at the location where the closest enemy was when it got in range, without trying target prediction or hitting as many enemies at once. This means that despite the large area of effect it will just miss any melee enemies if you let the AI use it. You can override the ability provided that the fireball has not left Thalya's hand, but beware, the moment an enemy that fights back is in range and the skill is availble (and Thalya doesn't have other orders) the AI will use the ability.
As for her other ability, summon shadows, unlocked at level 4, I personally don't see it as hugely valuble. Yes, its quite a nice, useful ability to have, but not worth spending lots of gold and evilness to get. And yes, I mean lots. One of the best things about Thalya is that she is availible at the start of every mission and can deal with a couple of basic threats all by herself. She is also the only non-demon troop that has passive regeneration, like the demons she must not be hurt for a while before it will start, but it is much slower than demon regen. Don't expect her to be able to deal with many of these basic threats before she dies. If she does die, she will resurect after a while (yay) and this can be sped up with gold. This costs 100x Thalya's level.
Horde Creatures (Combat)
Horde creatures are undeniably the strongest and tankiest regular troops. It is entirely feasable to beat most levels with only horde creatures. On the other hand, death is permanant for them without a very late game technology
Orcs embody everything I mentioned above about horde creatures. They do pretty good damage even at level 1, and have enough health and armor to be tanks early game. With the support of nagas and Thalya, they will kill very efficiently. With some mid game tech, they can become ironhides that have insane armor and the taunt ability that means weaker front line units like zombies and banshees will not be hurt as much, though the gunner enemies are still a problem for said units.
To start with, I am glad that basic goblins actually serve a purpose in combat in this game. Goblins have the lowest health of the horde creatures, but they do lots of damage, unlike in the predessesor to this game. They also have the inconspicous trait, meaning they are the lowest priority target for enemies even when they are being hacked apart by one. They can be used to assassinate back line enemies during a battle like novices or wardens and their upgraded versions. However, if this way of fighting doesn't work for you, you can instead get gob-o-bots that have an area of effect attack and higher health. They lose the inconspicous trait however. The goblin won't even die with the mech. They get ejected and can either continue fighting as a normal goblin (with the inconspicous trait) or retreat and pick up a new mech at the hideout.
Nagas are the healers of the horde. They have lower hp than orcs but higher than goblins, but their attack is terrible. They aren't availble with orcs and goblins, instead having an entirely different research for them. A naga will heal a target constantly if near an injured horde creature, converted hero or Thalya until they are at full health or move out of range, however, they will never heal themselves unless ordered to. To avoid annoying micromanagement I would advise always having at least 2, and you are unlikely to need more than that unless you spam horde creatures. Nagas also cannot move without stopping healing unless pushed by other creatures. Unlike the other two main horde creatures, they do not have an upgraded form.
Horde Creatures (Work and Rooms)
Horde creatures all need a free 2x2 space in the hideout each. This is where they rest and heal after combat and if a naga wanders into the room you may find that they just fire their healing beam at a resting troop and massively increase the rate of healing. Unfortunately, healing with just the beds is very slow, much slower than undead, so getting nagas is a priority. Even with an upgrade you can get from the lecture hall, it is still quite slow.
My typical hideout when full (pre ogres).
Not much to say about this. You can throw creatures in here and they will stay on patrol in that room, attacking any enemy who enters their vision range. You can also place a drum to call all creatures to the room, but only if you hit it. Considering how you can just pick up every creature in the dungeon and throw them on top of the enemies, this room is kind of useless. The only reason to research it is because it is a pre requisite to nearly all the horde research, with the exception of the hideout and nagas.
This room is a bit of a mixed bag in terms of its worth. In some levels there is no need for traps so the research is nearly pointless. However, in others, particularly in hellish difficulty, it is invaluble once you get all the powerful traps, but you need the lecture hall to get most of said traps. The most usefull trap is easily the rolling stone because of how much damage it does and the fact that it stuns enemies (not to mention you can do it on your own creatures including little snots which is fun). For this room to work, it needs a tinkers machinarium (how do you even pronounce that?) which takes up a 3x5 area unlike most buildable work units which are 3x3 so keep that in mind. You need orcs or goblins to work here. The advanced versions of them work faster, and goblins are faster by default so that's also worth remembering. It's also a prerequisite to gob-o-bots. As a final note, the blackboard on the machinarium will show a silhoette of what is currently being made and the silhoette will fill up with white as the trap or door completes.
The brewery is used to allow horde creatures to advance past level 3 where instead of being semi-powerful troops that die if you are unlucky / unattentive, they actualy have some suvivability without constant healing from a naga, but you still want nagas anyway. As with all the buildings that increase the level cap to 10, it's the research that allows the level cap to increase, not the actual building itself, though you will need it to satisfy the new needs of the horde once they reach these higher levels. Orcs and nagas can work on the brewing kettle, though it is usually preferable to have snots do it because you have more of them. Also, you can slap the stacks of barrels to send them flying across the room which can actually allow you to get a couple of extra barrels that your storage wouldn't normally allow. On top of that it's just funny :)
One of the most useful rooms, the arena is where horde creatures will constantly train to get more powerful. You can order other factons or converted heroes to train by dropping them in the room if there is an unused fighting pit, but for every bit of xp they get, you have to pay gold for it. One annoying thing is that you can't train pack creatures. WHY? It makes it a nightmare to level them up, involving rolling stones leaving small numbers of survivors and then dropping just the pack creatures on the survivors to power level and it's just a mess.
Demons are the only faction with the standard units comprised entirely of ranged attackers. They are also the only faction with a resource cost associated with the actual reviving (not the cost of what you use to revive) unlike the horde who die forever until you get the crypt where they are revived for free outside of the cost of the room and undead who can't ever properly die. They are the only producer of mana, used for spells, and they have a couple of other nice features mentioned later on.
Imps are probably the best demon fighters because, despite dying very quickly if ever attacked, they have high damage and insane range that allows you to draw out individual heroes from a group if played correctly. They also deal burning damage. They are the only demon avalible initialy, but they can be really powerful. With correct placement and the right upgrade (hint hint cough cough), they can outrange towers and even the extremely dangerous catapult, rendering those defences useless. Two of them make a great addition to an army, able to deal a high amount of damage, and their AI is pretty smart at targeting, often going for irritating back line units such as novices or preists. And even if they don't you can just tell them to and they probably won't be anywhere near the melee combat at the front, so they should be safe.
Succubus are ok fighters, with the beguile abilty that allows them to temporarily convert any enemy unit (yes any except bosses) to fight on your side. The only problem is that they will usually target front line units with this ability and your units will still attack converted units on the same priority as normal ones. That can be problematic. The standard attack of a succubus is a weak ranged attack not all that different from a naga's attack in terms of damage, range, attack speed and travel speed. However, succubus (what's the plural for this word?) have a surprising amount of health and like all demons will revive with mana after dying. They are also the only demon to work in the torture chamber...
Demons (Work and Rooms)
The vortex is the demons place of reviving. They do not need it for anything else, but they each need a 2x2 space for a portal. If they don't have one and die, they will lie on the ground where they died and eventually rot into nothing (or return to hell, it makes no difference). If they do have a portal and die, then they will almost instantly return to the portal and go into stasis where they will use a steady amount of mana to revive. If they don't get the mana they they will just stay in stasis until they do, beyond your power to really get rid of them.
This is the room where all mana is produced, but you need a mana shrine to actually make mana. One thing worth knowing about the shrine is that although it needs a free 3x3 space to be made, the corner tiles of this space are still used to store mana. Outside of this there isn't much to say. Each tile stores 25 mana until you get the lecure hall upgrades and each shrine can have 2 demons working on it at once (or 4 if you have the magic toolbox version).