There were some nice levels, and a lot of variation in mechanics for a game jam game (including the cannons, and getting a cannon yourself for the boss fight - yay!). The sounds are nice, and slightly scary ;-) (especially the skull's "DIE!").
Some tips: the arrow controls are inverted when standing on the left side of the screen. I tried it earlier, and it didn't run on my low resolution laptop screen - the minimum resolution is relatively large. But now I tried it again on a bigger screen and it worked.