What a LÖVEly entry, the artwork and music is great and gameplay is fun, good work on the sequences in between challenges. I did have a hard time with the Joker, which remains unbeaten.
Edit - Ok I just figured out you need to press the keys in the order presented. For some reason I thought the pop-up keys represented which of the characters the joker will attack, and you had to guess which of the three it was.
Nicely done!