Good game! The only negatives I could think of is that it isn't super obvious where you spawn the skeletons. I know that there is a tutorial, but maybe next time you just click the card and it spawns them there? Or maybe, when you are selecting one it greys out the rest of the map or highlights the spawn platform?
Also maybe add a fullscreen button when uploading the project?
But it was a very fun game! Good job!