Marvel Cosmic Invasion is getting a new story expansion centered on Fantastic Four nemesis and Avengers: Doomsday poster boy, Doctor Doom. The Siege of Castle Doom arrives in the retro-inspired cooperative beat ‘em up this fall.The Siege of Castle Doom is a paid DLC described as a new game mode that places Doctor Doom front and center, but with no trailer or screenshots, there’s no word on what he’s up to. We do know that the DLC will introduce two new…