The Deadric Princes thanks to a stupid Nigh Omnipotent mortal are teleported with their full powers granted while inside their realms into Marvel verse and start to create Havoc and destruction.
Mehrunes Dagon start changing the laws of reality and creating natural disasters.
Molag Bal start enslaving incalculable ammounts of mortals.
Hearmenus Mora start killing people and stealing knowlodge for his library.
And the list goes on.
Whomever at a certain point, The Deadric Princes messes up with many demons from Marvel verse (such as Blackhearth and Surtur) and they start battling.
Battle happens outside everyone realms.