Successfully complete the game with a 100% completion to unlock the cheats after the credits.Ragnarok Assault Mech in Multiplayer mode
In the "Divergent Entry" mission, climb the wall to access the second area. Look to the right to find a locked bunker. Use the access terminal on the left side of that bunker to play the hacking mini-game. Successfully complete the game to unlock the bunker, which contains the Ragnarok Assault Mech. Use that mech to complete the level to unlock it in Multiplayer mode.