Spare a thought for the person responsible for turning game features into Marketing Points™. One of the things Batman: Arkham Knight [official site] brings to the series, along with loads of Batguns, is sections where Nightwing, Catwoman, and others join the fray as AI partners you can switch between.
So here, look, it's a new video showing off the feature that surely dozens of hours of meetings and agonising and focus testing named Dual Play Combat.
At certain points, Batman will team up with a Batchum to beat the heck out of even more men than usual. The other character's AI controlled, flipping around and doing their own in ways you won't need to worry about, but you can switch between the two Batfolk at will. Perhaps your Batpal is in the perfect position for a mega-combo-a-rama. Or perhaps you simply want to be Catwoman and spin around.
It's a poor substitute for co-op, and mostly reminds me that co-op would be super cool, but hey ho.
Sadly this here video of Batman and Nightwing punching men cuts off shortly before - I imagine - Batman shakes the former Robin's hand and says "Thanks again, old chum." If I don't see that happen in the full game, which is due to launch on June 23rd, I shall be sorely disappointed.