Arch rivals Bahamut and Leviathan can take down Tiberius together if you purchase a Hard Corps: Uprising downloadable content pack.
The Leviathan DLC which Konami released on Xbox Live today makes the enemy character an ally. While Leviathan only has one weapon slot, he has a backflip grenade throw and a sliding attack. Screenshots those attacks are below plus pictures of the two other DLC characters Harley Daniels and Sayuri.
Like the other downloadable characters, Leviathan costs 200 Microsoft Points ($2.50). Hard Corps: Uprising costs 1,200 Microsoft Points ($15) and will be released on PlayStation Network next week for the same price.