Dual boss battle
Remember the David vs Goliath mutator from worms 3D? basically, one of your teammates had a stuffload of health, while the rest didn't have as much. It's basically that. Bring down the enemy team's boss to win.
A PROPER loving KNIFE FIGHT
No bitchass butterfly knives or grappling cru- er, I mean hooks, and no floating platforms either. Just the combat knife and a better map.
Character battle
Already explored in a few servers. It's a standard DM with any gamemode, but you have characters, and not classes, similar to DOTA, or whatever.
The first requires a slayer gamemode, sadly.