Now this is darn good for a jam game! Fun, solid concept, cool implementation of the powers (I'm particularly impressed by Fishboy's one), very well-designed level, and even destructible terrain. You could definitely take this concept and characters and use them for a full-length platformer.
No real downsides, just some minor things I didn't like so much. I found some of the sprites a bit ugly with their broad heads and big noses, and the menu is rather basic-looking, but that's just a taste thing. Also, Electulence's power was a bit juvenile for my taste (and is there a typo in his/her name in the menu?). On the upside, I loved being able to play as a slime monster, even though that playthrough was a bit frustrating (more about that below). Would have been nice if dying made you reset automatically, without having to press R. Unlocking new heroes seems a bit random, but that just adds to the fun in experimentation.
OozBoy's playthrough had me stumped for a while. SPOILERS BELOW
maybe I was just obtuse, but it took me a while to figure out that the ladder in the cave was climbable by jumping.
END SPOILERS
Like I said, those are all minor negatives, and I wouldn't nitpick if I didn't think the game was good enough to be worth it. I haven't played all contest entries yet, but this one is a high-water mark. I haven't found all the heroes yet; might be back with more feedback when I do.