Level design was really impressive here! I think it was tough at times to figure out which tiles were background and which were foreground and at one point in the second level if you fall off it deals a single heart of damage and doesn't kill the player right away.
I love that the enemies like the mushroom duck and shield themselves that's really cool; and that the giant bat follows more aggressively when you hit them. The "upgraded" enemies idea is also well implemented with the darker bats.
Great job!