Hungry Sumo is a great Flash game. You have to turn all the Sumos on the screen into friendly Sumos, and you do this by bumping into enemies until they are so small they transform. Your Sumos float around at random, and lose weight every time they bump into an enemy sumo, so you have to feed them by hovering over them with your mouse.
However, If a sumo bumps another while feeding, it will immediately be transformed into an enemy! Hungry Sumo sounds a lot more complicated than it really is, but once you get it, it’s really hard to stop playing! The graphics are cool, and the music is excellent too.