Tighten it up
The animation is a really good start, but the action wasn't terribly exciting. [Spoiler] It was just watching characters come on stage and then die in the pile. Some things that might liven the next one up:
1) A plot. Even though it's just a melee, the characters could still talk about something. The laughing was a good start.
2) Speed up the characters. If this means you have to simplify the drawings, it might be worth it. (If so, consider stylizing them.) Watching them stroll slowly onto the screen then fling an arm, slowly, wasn't really exicting. Speed up the time between battles, as well as vary the time of the battles. Almost all of them seemed to be equal.
3) Add camera perspective. Consider showing the battle from different angles, as well as a first person perspective from one of the fighters. Use zooms as well to dramatize the battle.
4) Add a background, or setting that can be destroyed with the characters.
5) Do something with the bodies. Just piling them up really took away from any depth the movie could have had. The characters coming on screen didn't acknowledge the 4' stack of corpses, didn't slip on the blood, and didn't have to move around them. Maybe they could decompose in some interesting way, or a few could be thrown into the background.
6) A little soundtrack with some upbeat music could add a lot of flare to the whole movie. Just don't use repetitive dance music :> Music from a movie will have enough dynamics to aid the characters with varied actions.
Overall, good start. I really liked the movement of the capes.