Snuff

It's impossible to get this achievement legit way. Night forest level is highly impossible to complete with 1 life. Sometimes Cultists spawn at the same time in front and behind you very close so you physically have no time to to shoot both of them. But even if you're ultra lucky to get to the final level, the last BOSS Belial is 100% unbeatable without many tries. When he spawns enemies with katanas, the game lags that hard so you can't move for 5-10 seconds. And it doesn't matter how tough is your PC, the game will lag anyway. When it finally stops lagging there's a very big chance you'll be already killed by katana guys. So the only way to beat the game on SNUFF difficulty is to press ALT+F4 right after you die to exit the game. The save file won't be deleted this way so you can continue from the last checkpoint and try again and again until you finally beat the BOSS.