How boring to use only Isaac right? Don't worry, following this guide you will be able to unlock all the characters that The Binding of Isaac: Rebirth makes available, which with expansion Afterbirth they even reached thirteen.
Base Characters:
- Magdaline: You must have seven or more red hearts at the same time
- Cain: Collect 55 or more coins in a single match to unlock it
- Judas: Defeat satan to get Judas
- Eve: Avoid collecting hearts (of any kind) on two consecutive floors
- Samson: Defeat two floors without taking any damage
- Azazel: Obtain three items from pacts with the devil in one game
- Lazarus- Collect four or more Soul or Black Hearts in a single game
- Eden: Defeat Mom's Heart
- Lilith (Afterbirth)Complete Greed Mode using Azazel
Secret Characters
??? (Blue Baby): 
- Obtained by defeating Mom's heart ten times
The lost:
Here the matter becomes complicated, there are two distinct procedures, one usable only if you do not own the DLC and the other can be used if you have bought Afterbirth.
Rebirth method (Not usable if you bought the DLC), follow these steps in order, if by any chance you break the chain, start over:
- Isaac will have to die in Basement or The Cellar, at the hands of a Mulliboom
- Magdaline will have to die in the Caves or in the Catacombs with one of her bombs
- Judas will have to die in the Depths or Necropolis from a mother attack (minions summoned by her are not worth)
- Azazel will have to die at the hands of Satan in Sheol. (Dying using the bible will ruin the whole process)
Afterbirth method, much easier (It is worth spending these 10 euros just to save yourself the process listed above ed.):
- Just find the Missing Poster and die in a sacrifice room with this item equipped.
Keeper (Afterbirth):
- Donate 1000 coins to the Greed Machine, which will appear once Ultra Greed is defeated.
