There legal issues surrounding Wonder Girl, but not any more. From Producer Greg Weisman’s blog: “There is NO LONGER a legal issue about Wonder Girl. But there was when we originally developed the series.” Maybe Wonder Girl won't be on the first season, but will join in the second season if the had produced the episodes of the first season. It could be Zatanna. Beast boy might just make an appearance for one episode, as the voice actor is a 10 year old.