I tried every strategy I could find online to get this achievement, but none of them worked for me. In the end, I figured out a way to get the three biohazards and thus the achievement. I repeated it a few times to make sure it wasn't a fluke, and it worked every time. Hopefully this will help anyone else who's stuck, trying to get this achievement.
Guide to Get Complete Black Death Achievement
This strategy works best on casual mode. There are other guides by other people about how to beat brutal and mega brutal. This guide is specifically about getting three biohazards and the achievement.
As the game relies heavily on a random number generator, this will take a bit of luck. But this does work, and it’s how I got the achievement. You ultimately need your final score to be above 7000. To achieve that score you need to keep cure progress down, infect quickly, and try to finish within a year of the start date.
You’re going to need a lot of DNA in the beginning. This disease starts off with a bunch of lethal traits that you can’t devolve and those will get you noticed almost immediately. You need to spread as far as you can as soon as you can, and this will get you the DNA you need to start off strong. Some people like ATP boost but I find it just doesn’t get you far enough.
Part of your score is based on how far they’re able to get with the cure. If you can keep that below 50%, or ideally below 25%, you’ll have a much better chance of getting the score you need.
Your biggest enemies in this scenario are the islands. Greenland, Iceland, New Zealand, and the Caribbean can and will block your path to victory either by not getting infected at all or by slowing you down past that year-long mark. The more we can do to guarantee they get infected quickly, the better.
We want this disease to spread far and fast. Here at Plague Inc, we believe in equal opportunity pestilence.
I’ve seen some people recommend Sympto-Statis, but this disease mutates symptoms quite efficiently and this strategy doesn’t require you to buy any symptoms. Trans-Stasis might also work, but Patho-Stasis is what I went with because you’re going to need to buy a whole lot of cure-delaying abilities, and you’ll need to advance through the three stages of yersinia pestis.
Getting Started: Starting Country and First Evolutions
Starting Country: India
I tried Saudi Arabia a few times, as it’s usually my go-to, but ultimately the plague just didn’t get going quickly enough whenever I started there. You can play around with your starting country if you wish, just make sure it’s a hot climate and has a seaport.
Wait until you have enough DNA points (it should only take a second, but keep an eye out because you need to get this as soon as you can!)
It’s your easiest, cheapest way to get this plague going. I went with this rather than fleas because you’re going to need rats in order to access other animal transmissions, so you’ll have to get it anyway. Might as well save that DNA rather than wasting it on fleas when you ultimately don’t really need them.
Once you have enough DNA, evolve both of these as well, in any order:
Livestock 1 (I usually do this before birds because it’s cheaper).
Soon after you evolve those, you should start infecting a few other countries. Keep an eye on your DNA, because you need to move forward as soon as you can. You may also see some symptoms evolving at this point - that’s a good thing! Just take note of which ones are popping up. If it’s something too fatal, you’ll have to devolve it so it doesn’t kill everyone off too quickly.
Once you’ve collected enough DNA, evolve the following:
Pneumonic Plague (you need to evolve this to gain access to further transmission vectors).
Water 1 (We want to get on those islands, asap!)
Even before you’ve evolved all of those, you should notice many more countries becoming infected. Thanks to our good friend Metabolic Jump, each of those newly infected countries are a goldmine of DNA for us to use! At this point, I would save at this point, just in case any islands manage to give you the slip. Better to pick up from here than right from the beginning.
The Island Dilemma
The next thing we’ll be doing is a failsafe for our island friends. We wouldn’t want them to feel left out, after all. We need to get Extreme Zoonosis so we have a chance at “non-human infection” of any stubborn stragglers. So as soon as you can, get the following in any order:
Once you have that, you’re done with transmissions! Bear in mind that due to the nature of this game and the reliance of the RNG, you may end up with an island that just won't play along. Unfortunately, if it drags you past the year-long point or just never gets infected at all, you're going to have to try again.
Time to move into abilities! At this point, you should still be raking in the DNA points due to the increasing number of infected countries, so update the following as soon as you can:
Cold Resistance 1
Drug Resistance 1
Cold Resistance 2
Drug Resistance 2
At this point I would save again, but I'm a compulsive saver. Save at your own discretion, but if you want to play it safe I'd recommend dropping a checkpoint whenever you finish a section.
Let the game play out for a bit as you pop bubbles and infect more countries. At this point, the cure has almost certainly begun and is very likely progressing quickly. You don’t want to let it pick up too much steam. As you build up DNA, pop back into the abilities screen occasionally to throw them off.
Genetic Reshuffle 1
Drug Resistance 3
Genetic Hardening 1
Genetic Hardening 2
Hardened Reshuffle 1
Hardened Reshuffle 2
Remember, the cure progress counts towards your points. The lower it is by the end of the game, the more points you get from it. It has to be under 50%!!!! 25% is the ideal, but under 50% should do the job.
At this point in my game, all countries were infected. If that is not the case for you, check to see which ones are left. Like I said, there will be some luck involved, especially with those islands. We can nudge things one way or another and increase probabilities, but the random number generator ultimately has us at its mercy.
If you’re a lucky bastard and all countries are infected, a bucketload of infectious symptoms should have evolved by this point. Once you feel that your disease is spreading quickly enough, let all hell break loose.
Make sure you have a solid, reliable foothold in every country before you evolve the following, otherwise you might kill people faster than you can infect them:
Total Organ Failure
You likely will not be able to evolve all three of these without devolving other things. When you feel comfortable with how far your disease has spread, start devolving your transmission vectors. You’ll get refunded two points for each one, and that should allow you to evolve all three of those lethal symptoms. Depending on what may have mutated, Dysentry may be a viable option as well. Basically you just want everyone dead before a year has gone by.
I tested this method multiple times. I got all three biohazards on each try, but it only worked on casual. That counts for the achievement.