I think a Miami level would be pretty cool. So would Pandora, and with Homestuck there are a lot of choices. I'd want Alternia, but considering this is B1 Jack, I think Derse or one of the Kids' lands would fit better. Or wait, did you mean a world that's a combo of all the fandoms the characters come from? That would be interesting, but also kind of a Clusterfuck. Still, it'd be cool. 

As for a zombie level, I vote Dead Rising.