Mikee's vague ideas
Most of the below could be incorporated into any round-robin game, and I could see an entire round-robin built around Mystery Solvin' Teens, as each one is an episode.
Rehash of an earlier Halloween idea. You're all Mystery-Solving Teens, with a sort-of-talking animal sidekick! Once more, funniest if everyone plays some kind of caricatured archetype.
Vampire Political Intrigue
There are two major alliances in the factions of vampires - the Sparklies and the Non-Sparklies. As the Sparklies attempt to gain power, how will you deal with them?
I am Zombie
You all wake up dead. How do you adjust to your new life as a zombie, with an uncontrollable appetite for brains?