Playing with two different characters was definitely a nice addition to this game. This is a fun game and I liked exploring the map and unlocking abilities.
The environment seems a little too "big" for the characters, that felt a little weird but nothing too problematic. The bullets from some enemies were hard to see. Maybe the characters could be larger or the environment could be smaller. The map was a little confusing. I think more visual feedback would really do good on this game (like enemies flashing when hit or something like that).
But other than that, I like the enemies and characters, they're full of personality. The boss was interesting but a bit on the easy side! The music matched the game well, and the style is interesting. Good job!