The sprite animations are really well done, I like the skull rotating, the character has a lot of personality and the bats are a cool design. The bat detail is a bit hard to make out, I would make the eyes or other details a bit brighter so they stand out more. I really like the below ground areas in the second level, that adds a nice reward for exploration. The design of the horizontal moving enemy is a little less clear, they kind of look like flamingos, but they also have a component that looks more like machinery, are the robot flamingos?