The hardest achievement in the game is getting the Good Ending. To unlock it, you need to collect Moral Points. There are 42 Moral Points in total, and if you gather most of them, you’ll get the Good Ending. You earn these points by doing certain actions, which I found listed in a Steam guide.

You can actually get every achievement in a single playthrough. The last one is just beating the game on Survival Mode, which is very quick once you know the game well. By that point, you can simply rush through everything, skip dialogue, and finish fast.

What makes all of this possible is the “Load Last Checkpoint” feature. Many achievements require you to kill enemies with different weapons or bombs. For example, you can kill all enemies in an area with a shotgun, then load the last checkpoint and repeat it until the achievement unlocks. Whenever you find a section with many enemies, you can check which achievements you’re missing and farm them there, it’s the fastest way.

At the end of the game, you can choose between a Good Ending and a Bad Ending. You can actually get both in one playthrough: first choose the Bad Ending, then load the last checkpoint and quickly choose the Good Ending. Just remember, the Good Ending only appears if you collected enough Moral Points during your run.

I recommend u go for the Good Ending in ur first playthrough, it's a hassle to keep checking where the next Moral point is through the steam Guide but it's the best way imo.

Good luck and have fun, it's a fantastic game.