Both Mom and Satan win, and Isaac's soul is claimed by Satan, that's a fact so far. The game isn't happening in Isaac's head either IMO, a child wouldn't know what a Pentagram is, what a Mark is, how to sign a Contract with the devil.and so forth, IMO, Ending 15 makes thins very clear, Isaac's mom was indeed hearing voices, the fact that Mega Satan is the ultimate final boss would indicate that those voices were from Satan himself who wanted to corrupt Isaac's soul, which he does, as shown in Ending 16. I honestly feel people overthink this too much, I think the game isn't as ethereal as people make it out to be, grandet the first Isaac was too ambiguous, but Rebirth kind of puts things on the table for good.

OR maybe he just went pure evil (mega satan ending) and thought that his mom's misery was because his dad left because she went crazy so he went to kill him, explaining the missing poster. These characters are isaac's inner thoughts (except maggie) because his mom is abusive and blames everything on him, he either ends up running away or killing himself, relating to the missing poster ending. well, thing is, i dont know how the other characters are in the bible, according to you they are bad people so we can add up our theories. Now the more i think about it, maggie might actually be isaacs dead sister, blergh. Originally posted by Graysparv:a good theory, but i still have this belief that the other characters are his different personalities cause of his mom wanting a grill (maggie, eve, eden) and calling him unclean (azazel, judas and cain, scum from the bible), and him trying to fight it (samson and lazarus, warriors and saints both from the bible) and eventually killing himself or end up dying.

The lost binding of isaac