Riddler x Robin
The riddler sat in his cell in Arkham listening to the guards on their nightly rounds, the even strides, the crakle of walkie talkies, the clatter of key cards. (they finally found out that regular keys were a bad idea around gothams greatest criminal minds.)
He was also thinking about (what else) getting revenge on bat man… now that he was thinking about it, more often than not the bat had only succeded against him because of his domino masked assistant. Yes… now there's an idea… robin is if not the only reason, at least a major contributer to foiling his attmitedly brilliant scemes. So if he took robin out of the game… batman whounld kill him and dump his body in alleys from here to metropolis.
So killing him is out of the question. 'kidnap then?' he pondered 'just put the kid in time out (not a deathtrap) then while the bat was out hunting for the bird, he'd do his heist, or two and act normal (as normal as you can get for a guy who robs museums in a green cat suit any way.) and pretend like he had no idea where robin was or even that he was missing.' He smirked in the gloom 'Perfect.' Now to get his slick mitts on one of those key cards…