Check out Super Mario Wars for a quick mario deathmatch fix. Mario with guns? Not quite – run around trying to leap on the heads of your opponents, grabbing powerups and avoiding environmental hazards taken from mario’s 2d adventures. It’s a bit…hyper for my taste, but it’s fun in 5 minute doses. It’s available for PC, linux, xbox, and Mac (check the forums for the mac version). Free, open source, fun.