I really like the aesthetics - the character designs are cute and the overall vibe has a lot of charm.
The mechanics were also cool - the buttons that shoot the other player up if the other player ground pounds was really creative - love that.
I would say I wish there was a more forgiving checkpoint system, or the characters had a few hitpoints rather than dying in one hit - with 2 characters there's twice as much chance to instantly die ;) I found myself repeating the beginning of the level a lot which got frustrating, especially when I died from offscreen spikes a couple of times.
Overall great entry, especially for a 1 person team!