What is Remix? You get assigned another author and you get to pick one of their stories to remix. That means you rewrite their story, but from a different POV or in a different setting, or maybe set before or after or taking a short fic and expanding on it, etc. You have to leave the pairings the same and the basic plot, but otherwise you can do whatever. In turn, somebody else remixes one of your fics. The exchange is anonymous, so the remixers identities aren't known until the fics have been posted for a little while.
Who can play? To qualify, you need at least five fics of 500 words or more in a single fandom (so that somebody has some hope of remixing you), although this year they're thinking about changing it to allow at least 7 fics of 100 words or more instead. Otherwise, anybody can sign up, but the catch is that a certain number of people have to be in each fandom for it to work, so before signups, they do a poll of who is interested in each fandom, and the fandoms with enough people are the ones that you have to be able to write at least one of.
But on the other hand, once you get a assigned a person, you can remix any of their fics in the whole world, even if it isn't in one of the fandoms you signed up with. Authors get to pick one safe story that you can't remix, but otherwise anything goes.
Why are you telling me this? I'd really like to do either JE or DBSK in this year's remix, since it's the first year RPF might be allowed, and it's all I'm really writing these days, and there's a lot of authors for both on my flist. right now on the poll there's only 4 people signed up for DBSK and 3 for JE, which isn't going to be enough for it to count.
So, if you're at all interested in Remix, go vote in the poll. The poll isn't binding or anything, they're just trying to see which if any RPF fandoms have enough writers interested to play.
I want to play this year! Don't make Gackt-chan cry, guys.