Very nice for a first game! Some things to note:
-Turn off font anti aliasing, for a pixel game it looks rather weird. ("Blurry").
-Consider adding sounds for the Turtle Fairy's textbox.
-The attack sounds for the bats keep playing after death.
-Attack (x) seems to not do anything? Not sure if this is just me.
-The "Space to try again" screen sometimes doesn't disappear after respawning.
Consider adding a save feature, but I know this is just a demo.
Overall, very cool! I love the menu and the music!