I got back to playing Binding of Isaac recently, and I managed to pull off one of the hardest achievements so far: beating Mother with The Lost. Though I lucked early into a ludicrously high damage, high fire rate build, the run was tense all the way through because I found zero revival items until the very last level. Which was Guppy's Collar, which was still only a 50% chance of revival on death. I can't remember the last time I was to tense during a boss fight, because Mother definitely leans heavily into the bullet hell aspect of the game, and some of her attacks can fill the screen with projectiles.