How long and how often are you allowed to borrow characters from other comics for? I'd love to see Babs and Dick get on the dynamic duo level as often as possible!

It totally depends. Usually, a guest shows up for an issue or two, the writers of their own books don’t want them to be two places at once, it can get confusing (how the bat-editors do all the coordinating, I have no idea).

Often, a character is simply not available.

But look out for a Nightwing appearance in just a couple months!