The game is really fun to play. But still could need some work. Imho the graphics are too simple. It took me some time until I spotted the coins. Making them yellow/gold would have helped a lot.
You can kill as much enemies as you want if you position yourself right on one of the higher platforms. Then just aim downwards and keep your muss pressed. But I think it is somehow ok because positioning that way is risky and you still have to collect the coins.
I like the idea that you become reborn as unlocked character. But it feels unfair that you directly spawn where you've died (or is it always at start? Not sure because there I usually got caught). Which means my other character dies at the very same spot and I can't do anything. May you could somehow reset the level with the new character.
Besides that the game definitively needs audio!
Overall a nice game with high replay-value. Good job!