Hardest achievement to get?

[Ponury Siepacz]

Personally I hated getting S score on They Bleed Ponycorns. At first i didnt even know how is it possible (got 5000 at best). Then i watched some walkthrough and i noticed you need x30 combo in the beggining. That was so frustrating to do, randomness and squids everywhere :(
Did it after 3 hours trying

At least, rest of the level is very easy.

I guess immortality/speedrun for 4:3 is hell

[alcrøwhol poisoning]

I'm starting to think speedrunning 4-3 is a test of sanity. It takes a lot of self-control to not throw the keyboard after dying just before the door.

[sayre85]

Far and away it's the 4-3 speedrun. The window for error is a fraction of what it is on the other levels. So much rage.

[Pink]

Shadow out of time followed up by Elder god.
Final stage speed run was definitely the hardest for me.