There are weekly challenges, you can find the rules on the profile (there aren't many, really) and the winner gets a pretty banner.
Basically you can make your drabbles with whichever fandom/pairing/character/book/movie/show you want. It doesn't matter. All it has to be is dark which is defined by you.
Dark as in no light, dark as in depressing, dark as in sadistic, dark as in masochistic, dark as in... whatever you understand by dark at the moment.