Mimiron is an encounter the Ulduar dungeon He created Flame Leviathan. (Which is another boss in here)
Phase 1 : On engage Mimiron immediately jumps into a vehicle called Leviathan MKII. Phase 2 : When Leviathan MKII is destroyed, Mimiron gets in VX-001, an Anti-personnel Assault Cannon. Phase 3 : When VX-001 is destroyed, Mimiron gets into his Aerial Command Unit. Phase 4 : Mimiron forms all of the other weapons used previously into V0-L7R-0N.