If you're playing the base Rebirth without any DLC, you've got to go through a specific sequence of deaths. And I mean really specific. Each step has to happen in a particular order, with particular characters, in particular rooms, dying in particular ways. Mess up even one part and you have to start all over again.

First, you need to die as Isaac in the Basement. But not just any death, you've got to be killed by a Mulliboom. You know the ones, those little guys that look kind of like Isaac but with a messed up face and a bomb sticking out of their left eye. They charge at you and explode. You need to let one of them take you out.

Second, you need to die as Magdalene in the Caves. And you have to die from your own bomb. Yep, you've got to blow yourself up. Make sure you're in the Caves, drop a bomb, and stand too close. Boom.

Third, you need to die as Judas in the Depths. Specifically, you need to be killed by Mom's foot stomping on you. So get to Depths 2, trigger the Mom fight, and let her foot squash you. Don't kill her, don't avoid it. Let it happen.

Fourth and finally, you need to die as Azazel. And this time, you've got to die to Satan himself. Not to one of his minions, not to the fallen, not to a bomb or a fire, directly to Satan. And here's the important part, dying to the Bible doesn't count. So don't try to cheese it with the Bible instant kill, because that's not going to work.

One extra thing to keep in mind. If you want to find the Missing Poster, you need to beat The Lamb as Isaac. That's how you unlock that particular trinket.

If you've got any of the DLCs, things work differently. Much simpler, honestly. You don't have to do a bunch of complicated character, specific deaths anymore. Instead, you just need to do one thing:

Die in a Sacrifice Room while holding the Missing Poster.

That's it. Simple, right? Well sort of. The tricky part is actually getting your hands on the Missing Poster in the first place.

The Missing Poster is a pretty rare trinket. It doesn't show up all that often, so you need to be smart about how you try to find it. Here are a few methods that can speed things up:

Spam the Mom's Box active item. It spawns trinkets, so if you can get your hands on it, you've got a much better chance of finding the Missing Poster.

Use Divorce Papers along with a trinket that gives you a similar effect. There's a specific interaction here that can help.

Reroll your run as Eden until you start with it. This works, but you're going to need a lot of Eden tokens saved up because it's completely random.

Now, Sacrifice Rooms themselves aren't exactly common either. They only have about a 13 to 15 percent chance of spawning on any given floor. That's pretty low. But here's a useful trick, if you enter the next floor with full red heart containers, the chance increases quite a bit. It goes up to about 30 to 34 percent. So if you want to increase your odds, make sure you're keeping those red hearts full before you head down.

Since I'm already talking about unlockable characters, I might as well cover the other two tricky ones while I'm at it.

The Forgotten was added in the Afterbirth+ DLC. To unlock this character, you've got to go through a whole process.

First thing you need to know — before you can even start the unlock process, you need to have beaten The Lamb. That's a prerequisite. No Lamb kill, no Forgotten for you.

Once you've done that, here's what you need to do:

Beat the boss on Basement 1 in under 1 minute. You've got to be quick.

After the boss is dead, go back to the starting room and place a bomb. If you did everything right, a broken shovel should appear.

Now, here's where it gets interesting. You have to carry that shovel with you all the way to the Womb. While you're holding it, Mom's foot will keep stomping down on you throughout the entire run. It's constant, it's annoying, and you've got to dodge it the whole time.

You need to beat Boss Rush and collect the second piece of the shovel. That means you've got to get there in under 20 minutes.

Then you've got to make it through the Womb and Sheol to reach the Dark Room.

In the Dark Room, you need to find a patch of disturbed dirt somewhere in the floor. That's where you use the shovel.

It's a long process and it's not easy, but that's how you get The Forgotten.

The Keeper was added in the Afterbirth DLC. This one is a bit more straightforward, but it's still a grind.

To unlock The Keeper, you just need to donate 1000 coins to the Greed Machine. That's it. But that's a lot of coins, and you're not going to get them all in one run.

What you need to do is play through Greed Mode, or Greedier Mode if you're feeling brave and beat the final boss. That's Ultra Greed if you're on normal Greed Mode, or Ultra Greedier if you're on Greedier Mode. Every time you beat him, you can donate coins to the machine. You just have to keep doing it until you hit that 1000 total.

It takes time, it takes patience, and it takes a lot of runs. But eventually, you'll get there, and The Keeper will unlock.

So there you have it. The Lost can be unlocked either through the old Rebirth method with the specific death sequence, or through the much simpler DLC method with the Missing Poster and a Sacrifice Room. The Forgotten requires beating The Lamb first and then going through a whole series of steps with the shovel. And The Keeper is just a straight grind to 1000 coins in the Greed Machine.

Each one of these characters is a pain to unlock in their own way. That's just how it is with this game. But if you're going for 100% completion, you've got to do it eventually. So get out there, die a bunch, and good luck. You're going to need it.