Submarine invaded by the Joker's sea-crew

In a bit of a face-off between two sea-crews. Possibly there were two submarines, one which belonged to me, and another that belonged to "the bad guys". "The bad guys" managed to board our vessel, and we were strategically moving around, trying not to get shot by them. Among "the bad guys" were the Joker (from Batman), and his boss (can't recall his identity; some regular human looking jerk). Everyone was running around, up and down stairs, around corners (this was rather wide-open architecture, as submarines go; not very subby at all, really, actually, also quite well lit). By chance, I ran into the Joker, primed my shotgun, and knocked him off. Fortuitously, his boss came up right behind him and I shot him down too. I called out to the rest of the invading crew and told them that there was no reason I should have to shoot anyone else. They became docile.