I got a funny bug that made my pebble have negative gravity and stick to the ceiling (or fly into infinity in the levels with an open sky)

However, I managed to clear the game and fly into the moon lol.

Improvement suggestions:

- Make the level clear condition more obvious. The number above the player head isn't explained and I spent a long time wondering how it worked. It could be a "global" enemy HP bar that gets decreased with each enemy kill and when it reaches zero it ends the level.

- Make negative effects more obvious in the upgrade cards. A different colored text is a good way to do it. I didn't notice the power increase upgrade reduced my ammo and after a while I was wondering why I could only shoot once every few seconds.

- Make remaining ammo more obvious. The little pebbles on the gun are very difficult to notice.  I'd suggest adding a separate big UI element on the screen that shows both the remaining ammo and the reload animation.

- Volume controls.

Good game!