Hi Malander, nice game! Here are my thoughts. I'm trying to help you get better, not criticizing your game for no reason, so don't take this personally. I enjoyed the game and it was worth the 99 cents
Also disclaimer, I only made it about 15 levels in before softlocking. On the level with the spike cross in the center and two skeletons below, I spawned with upside-down gravity and just fell to the ceiling. Restarting the game doesn't fix it. So that's where I got stuck and couldn't play further.
The controls were okay, but could definitely use some improvement. Sliding my finger between left and right buttons should make me walk left and right (see how VVVVVV does touch controls). The level design mostly required tapping one direction the whole level (except the level where you climb up 5 blocks, that one is very clearly annoying), which made this less noticeable, but I think better controls would allow for more interesting level paths. Also the jump button was small and way off to the right and I missed it sometimes.
The player physics were decent. It's annoying that you get stuck if you fall while rubbing against a block
The graphics were quite nice, good job to the artist. I especially like the fox character with the moving tail. However I think the levels felt too zoomed out. Every single one has empty space around the sides that could just be cut off, and most levels could be compacted further. This would make the game prettier and easier to play as well. The music was nice and fitting.
The difficulty curve was out of whack. The level with the 5 skeletons was extremely tricky to navigate, the level with two yellow gate jumps was quite difficult, as well as a few others. I also generally felt the game was too hard for what the controls were like. For your future games, I'd recommend watching other people playtest your game more to help with balance.
The level design flow felt a bit weird. I think it'd be better to evenly spread out the introduction of new gimmicks throughout the game. As it is, you introduce them all at the start, and then there's nothing new to discover throughout the rest of the game which gets a bit stale. (I may be wrong here since I had to quit early) You also failed to introduce save points and water, which I think could use signs of their own. The signs were useful and succinct, good job there.
The game gave me the same water level with the spinning apples and spike crosses two times, one early and one later. Also the jump refreshers felt really small and hard to touch.
That's all the stuff off the top of my head. I hope I'm not discouraging you at all. The game was enjoyable, and seriously, good job on even finishing a game, that's something not a lot of people can say.
Especially when you didn't even start with a GameMaker engine like most fangame makers do. If you continue making games, I wish you good luck!
If you want to update the game, the main things I'd recommend are: nerfing the hard levels (watching a playtester can help you here), zooming in the view, and improving the controls. You can also apply my feedback to future games. Also you're probably not going to get any more responses on this forum since it's pretty much dead. For the future you may want to post in the I Wanna Community Discord, invite link here:
httpss://discord.gg/SjpjuaH