There is a sweet spot with the boss, if you are ontop of the normal enemies you can just dash up and attack for free. The second attack kind of deals with that, but it only happens twice or so.
The dash up is an awesome move, but it wasn't intuitive for me and it took me a bit to figure out how to get out of the first hole.
The background in the dungeon/castle was a little monotonous.
I really loved the character art and the enemy art. The boss art was amazing and the background for the boss was equally impressive. Overall I enjoyed it and I hope you keep working on it!