Acually, you have to open the chest at the beginning, then not get the gem OR go up, go right instead, right through the wall.
Edit: it's extremly hard. Don't say I didn't warn you.
couldn't even get past first screen, screens are insanely long, near end uses OG celeste classic speedrun tactics and recreations of the levels combined into one screen
I couldn't get past the first screen in trueskip either, I can do the walljump part and the precise dash, but then I always died