Here is how it would work. It would be a coop game, with up to four people playing (or having AI buddies). The battle would be set inside a giant castle, with a thunderstorm brewing outside. It would have lots of creepy dungeons and dark corners, and be filled with ornaments that I could scale. I would be a stealthy boss, and this would be a game of cat and mice.
The players carry guns, but have limited ammo, and there is limited lighting in the castle. They will carry flashlights, and will get brief flashes of light from the thunder outside.
It would be a very long level, where players can try to take me down or escape the castle, neither of which will be easy.
Basically, imagine playing with three friends, all four of you are playing as one of the Joker's henchmen in Batman: Arkham Asylum, and the Batman just entered the area you're patrolling. Then you get the idea 







