Before you judge the thread, read through.
My idea is literally taking one team of players to pit them against another team of players. But not in character vs. character.
No, one team of players becomes "dungeon masters", are given a random dungeon, and must set it up and select their monster class and stuff. They have 5 minutes to do this while the other team waits in the entrance area and is given the chance to buff up and stuff.
DM team moves through the dungeon, setting up traps and areas of mooks. They're given a certain amount of resources to do this.
Then the "hero team" moves through the dungeon, fighting the monsters, but also having to deal with the red name monster players, who have picked their monster class (though one player picking a monster locks that monster out for other players, so they're not forced to pick just a bunch of beholders are something) and must fight them.
Dungeon scaling is in effect (so the larger the hero team, the more boost the mooks and monster players get, but the LESS heroes there are, the the more boost the heroes get) and such.
Obviously, this is just a rough concept, but what do you think? Somewhat inspired by Turbine's other MMO which has the "Monster Play" option for VIPs, only in this case, you actually set up the dungeon.