Okay, I came from your latest devlog and reached the end goal of each level. I assume you want feedback so here are some of my thoughts. ^_^
I think I found some bugs, firstly that reaching the end goal didn't stop the timer or end the level for any of the ten levels. Secondly, if I pause the game while the bird is still in the starting animation and then return to the game, I can move around as the ash sprite. Lastly, the first level seems to spawn the bird on the roof of the level.
The game has nice physics in my opinion, although I feel like something is off.
It wasn't initially intended to be a platformer speedrunning game though so that makes sense. On that same line of thought, the intro animation for each level doesn't feel right with the speedrunning focus, it seems a bit too long and not easy to exit right when I'm ready to play.
The levels were made quickly, so I won't bother mentioning everything that could be improved. I know with more time you could improve them. I enjoyed the tileset change on the final level, too. For someone who hasn't played before though, it could be a little easier on level 10 for example to work out which way I'm 'intended' to go. I never got fully lost, but it was partially guesswork for a few moments. (Although fixing the 'you spawn on the roof' bug would help with that.)
Lastly, sounds. I have a feeling these will change, haha, but the sound every time you jump could be softer or less dramatic if that makes sense, and the enemy hitting you sound could be more hostile. I think it's the same as one of the positive sounds. But I really think they're placeholders so whatever lol.
Thanks for uploading your demo, I hope my feedback is useful :]