ChallengesBrains I like the concept , but having to make it to the Chest as Blue Baby ends up coming down to RNG determining whether you win or not . Very frustrating challenge . Speed ! Again , your ability to win heavily depends on RNG . I ' ve beaten it on two save files , and both times I needed We Need To Go DeeperEwhaz to get the win . Cat Got Your Tongue theoretically not as hard , but BonesBlack Bones can fuck you so badly . CharacterThe Lost I originally got all his unlocks in Rebirth . That was the most unpleasant , frustrating experience I ' ve had in any game . After getting Holy Mantle , he ' s a lot more fair . Keeper Like the Lost , but with no upsides . More of just a slow , tedious character that can ' t take Devil Deals . Kind of doable once you get Wooden Nickel . The timed unlocks Hush and Boss Rush are nearly 100 % RNG . On my second save file , I just held R until I got Tech X so I could do Hush , and it was still a tough fight . BossKrampus can be very , very cheap . His spinning Brimstone attack isn ' t too hard in theory , but if he uses it while against a wall , there ' s literally no place to go . He can also move while using it . Generally any RNG attack bosses Daddy Long Legs , Conquest , Mamma Gurdy . Rag Man Not a bad boss , but he shouldn ' t show up as early as he does .