How about this.
Invasion.
The defenders own a huge mansion (guild house). Nervous of somebody trying to kill them, they have set up various defenses to protect against invaders. The attackers will have 5 minutes to kill the leader of the Defenders. The defenders have various traps they may use to stop the Attackers. They could use arrows to shoot at the Attackers, throw bombs, or use switches to do certain things as well. Leaders cant heal, so every number of damage on them counts. Once the Leader is dead, the game is over, and the Attackers win! If the attackers fail to kill the leader in time , defenders win.
Various changes could be made if one team is kind if under powered. For example, maybe the Leader of Defenders has two Body Guards that can protect them, and if they die they go into a tower? Maybe attackers get more time? I don't have the money to test this out, nor the friends to play this with. Just a thought.