Infection, team of 12 (or would that be too few/many?) players. All armed with a single white grade weapon that's the same for each and randomly chosen at start (no launchers so you can't kill yourself though) with supers disabled (maybe include disabled melee and grenades too?). Then after a short delay (only a few seconds so you can get away from your spawn point) one person becomes a Hive Thrall (the Thrall would have the same amount or near as much health as a Guardian so they have a chance of reaching the survivors)... From there it's simple either team infected/Thrall kill everyone and win or the remaining Guardians survive long enough to win the match