Congratz on a really cool idea, I love games with ingame editors, i'm building one myself.
Suggestions:
1. Maybe start counting the time on the level, only when the first movement is made, not when you click start
2. Auto-rotate landscape mode (both ways instead of one way)
3. It seemed like few tutorial levels kindof required double jump, before it was explained/introduced in the tutorial (or maybe it's just me with poor platforming skills :D )
4. The UI seems simple and nice, maybe the lives/time/fire UI on the top-left corner can be bigger (playing on Sony Xperia XZ)
5. Just a suggestion to make the jump a bit higher if the jump button is being held longer (like cuphead, mario (which you are inspired from as you said)
6. The difficulty really ramped up once i got to the 'Unstable ground' level, compared to the previous level (also a not i dont know if i still was on a tutorial or not, no indication how far i still need to go in levels to finish the tutorial.

One small bug that i found when registering in-game, was i entered my password, pressed 'new_line/enter' on the keyboard, the cursor went to the second password inputfield, and started writing in front of the placeholder 'password'. Nothing major just an observation.


This was all really nit-picking, really like the graphics and responsive control (no undesired sliding around). Experiencing no lags, so performance is great!

Just finished the tutorial, was probably too eager to write. Although some kind of progress inside the tutorial how many more levels are ahead is an idea. Also i noticed there is no indication how long the player is invincible after getting damaged (like getting a heart before the spikes, then i could on them for a bit, but i don't know for how long). Maybe some flashing player sprite like Mario is also a suggestion