10. You Can Spot Black Mask Right At The Beginning
Black Mask would have to wait another two years before making his full bow in a Batman video game, but he still has a small role to play in Arkham City.
Apart from being the main focus of Robin's challenge map pack, Roman Sionis also features in 'Arkham City Stories' - small anecdotes that fill in the gaps between Asylum and its sequel. They reveal how Sionis lost control of the Steel Mill to Joker, and they also detail his failed escape attempt. (Scan the sealed off tunnel on the upper north east side of the mill, and you'll be able to read what happened.)
Given Black Mask appears in DLC and is only referenced in the main events of the game, it might be easy to miss how he actually has a cameo during its opening. As Bruce Wayne is processed by the TYGER guards, you can see Black Mask fending off a couple with a chair, only for him to be overpowered and subdued. (Skip to the 5:50 mark in the above video and see for yourself!)
Canonically, the next time players see Black Mask in the Arkham series, he's being tossed out a window by Red Hood.