I'd also add to the post of Katerpie that the part around 0:34 is still feasible without keeping that sliding pose which I think is quicker to figure out that the intended strat. I'd lower that cloud one block.
Also, in the part starting in 0:39 and finishing in 0:57, you could also disable jumping if you want to keep that triangle and it's still possible to get past it only using screen scrolling and keep jumping ability for the rest of the level.
In 2:14 and 2:18 (along with the note block), those slopes feel useless when you're given a shell and should be removed, unless you find a way that forces you to use them.
And lastly, cutoffs in 2:39 and 2:50 can be fixed easily while the latter requires map16 shenanigans.
Anyways, that's a good level with an interesting gimmick!
Go fix your goddamn mobile app, YouTube!