This is definitely a skilled based one and i commend you for making a great mechanic!! It does really feel good when i recover all of my stamina quickly through the bird transformation. Love the 2.5 D perspective. I am a fan of that kind of art style!!
Some feedback:
1) After winning the game, the scene changes back to tutorial mode without any door to restart the game (screen shot below)
2) The indicator for the stamina regaining seems a little confusing as it doesn't feel too much like anything is regaining. It looks more like i am getting hurt. Probably because of the shape language and color (red = bad, jaggy edges feels dangerous)
3) It would have been awesome if I could hit downward or upward but that's more of a feature request than anything else!
You got yourself a very clever game here!! Hope that you're able to make more levels!