A ship's away team lands on an unexplored planet, to find something happy to see them.
At a secret research facility, a bizarre and terrifying creature is under study. One day, it escapes.
A DnD-esque adventuring party goes down into a dungeon, and are caught by the creature that lives there.
A demon pops up near an all-girls school, looking for some fun.
Could be either:
an all-female group is meeting(could be at a library, church hall, whatever) when something slips through a crack in reality, and finds them.
Of course, if anyone wants to do a scenario of their own, I'd be perfectly happy to do so.
EDIT: I forgot to say, I play free-form.
I live in the Near East, so while I try to post at more than once a day, the timing may be awkward.