Fix the sizes of the room (I believe it's the init room) so when you restart the screen doesn't shake. This forces the game to recenter to the center of the screen.
The first save shoots apples at me and then restarted me at the beginning of the room. It saved me in the room but not my x and y values. I'm sort of guessing this is 'intended'. If I died before this you teleport to the cut scene instead. I'm not sure which is intended.
Distinguish the difference between roll saves and regular save points. Most people do this but changing the text and making some funny troll that pops out but when I shoot a save without any indicators that just kills me it's not interesting, fun, or enjoyable in any way.
Why nerf the diagonal on the first screen?
The fake block(s) should be a block that disappears after touching. Not just a missing block.
Boss is kind of boring and extremely easy when doing it from the bottom.
The game isn't as hard as you think but making a hard game isn't necessarily fun to play. A game can be 'salt inducing' without being over the top in difficulty. Look at example games such as
I wanna go Bananas or
I wanna be the DareJar for examples since I think these are the type of games you had in mind for making.
Also please go to Global Game Settings and enable fullscreen on F4 press. (Resource Tab > Change Global Game Settings > Other > Check "Let <F4> switch between screen modes.")
Edit(s): Grammar errors and clarification.