I personally think it should be Batman because then their could be a hookup.
Van Kleiss and someone whose name rhymes with -oison Ivy.

Well, there's already Generator Rex & Ben 10 crossovers out there, believe it or not. Other than that, the Secret Saturdays and Teen Titans.

Poison Ivy & Van Kleiss, wow. I wouldn't have thought of that one. XD

I say Secret Saturdays cuz I'm already started a story for that