I've been watching lots of YouTube videos about speed running recently and have started watching a few about Celeste and it's genuinely incredible to watch what people have been able to achieve in this game. Absolutely blitzing through sections that destroyed me when I played it!
As that twitter thread from a while back shows, the mechanics of this are just so, so well put together that it really does raise the skill ceiling to the point where people are able to do some truly insane things. You can definitely see why the game has taken the speed running community by storm!
EDIT: This video is a great one for showing just how well the game is designed in terms of speedrunning: