Celeste was (to no one's surprise) challenging to beat using the keyboard controls, yet I have managed to complete all of the chapters (spare Chapter 9) and its B-sides! I'm doing a second playthrough using a Pro Controller instead, and honestly, that is way easier for me now that I don't get confused pressing which button is which and dying a lot.

Rain World, oh boy this game has caused so many deaths in terms of survival and exploration, many of them were either from me being dumb and not inputting things correctly or died to an unfair cause in some way. Despite the plentiful troubles, I have completed all 8 non-secret campaigns, one of these was beaten twice and the other I'm currently replaying! That said, this is likely the hardest game I have ever beaten.

Baba Is You is difficult in a different sense, instead of trying to use your actions to go from point A to point B, it's a puzzle game where you are required to use up at least 70 of your brain cells. I solved almost all of the 230+ puzzles and completed the game, at the cost of my brain being fried! :D

An honourable mention goes to Hollow Knight, which although is a game I do enjoy a lot and have beaten the main final boss at one point, I haven't actually gone through all the game has to offer, more so I have not reached the true final boss (I've been stuck trying to beat the colosseum) ^_^"

TLDR -- Most likely Rain World