How long do these fics have to be?
100 words or more.
Can we use stories already written for one or two of the prompts?
You're allowed to use up to five previously written stories. The rest have to be brand new.
Can we sign up with co-authors?
Are crossovers and AUs allowed?
Yes. I'm such a sucker for crossovers and AUs.
If we have a character claim, does that character have to be physically present in every fic, or can it be about them (ie other characters talking/thinking about them)? I'm mostly thinking about a case where the OC is dead or otherwise missing.
Your character has to be present in every fic. Remember...this is a place where the OC gets to shine.
Can a single fic cover more than one prompt?
No. 25 separate prompts=25 separate stories.