No doubt you saw Jeff Rients's Encounter Critical scenario starters early this week.
Here's a few I thought of by trying to rise to his level of awesomeness:
1) Inspector Gadget and the Power Rangers must team up to save Moses from the Borg Terminators.
2) The mogwais on the cargo deck broke into the crate of magic Jelly Bellys and now a tribe of evil monkey-lizards with super powers is loose on the ship.
3) Your Firefly-class vessel is set upon by Reavers--who turn out to be Space Hippies who grew up to be Space Yuppies in the Space Eighties and are just out to have some Brett Easton Ellis-type good times with their cocaine lasers*.
4) A lawyer from a supernatural law firm (Daniel Dae Kim) joins forces with a Minbari bounty hunter (Mira Furlan) and they travel to a mysterious island to bring a rogue gaseous lifeform to account for his pointless television show.
* "cocaine lasers" is from the song "Pobody's Nerfect" on the new Wolf Parade record, Expo 86.