The idea is fun, I quite like it!
The cards collisions are a bit off but they work out in the end.
The attack rate increase upgrade is op. Makes the game too easy.
There is also a bug with the attack of the cards, it seems like you used a collision area with a entered kind of detection.
If you go into a corner the cards will get stuck on you and you no longer get damaged.
It would have been nice to have a points system or something similar. But overall the gameplay is nice.
Well done! Keep up the good work!