Thanks for the critique, I appreciate it!
The nothing cards are to represent that you're just not very skilled at the beginning of the game and to junk up your deck. Replacing them with better cards throughout the game is how I model self-improvement. Originally there was no way to add cards to your deck, just replace them, but I finally added the burger stand when I decided the later levels were too luck-based with only 15 cards.
And yeah I'm not happy with the breathing animation either, it was a last-minute addition and this project was my first time trying deformation-based sprite animation.