This is a fun game. The level that comes after the one with 13 coins is really long though. I died before I could finish it. And it's hard to find the coins, so maybe a minimap or arrow that points to the nearest coin or something could help?
Hmm. I think it's too hard as the game currently is, but if something was added that made it easier to find the next coin, it would probably become a good challenge.
