To get ragenorock all you have to do is complete the game in novice mode(which is easy mode).

Unlock Ragnarok For Multiplayer
To unlock the ultimate Ragnarok mech for online/multiplayer, simply beat the single player Campaign mode. The Ymir variant will also be unlocked. Cheats [Submitted by: Micheal Turner]
These are very complicated cheats as time goes on there might be less complicated but for now these are the only ones that will work. 1. Press these keys in this order on the main menu of Mech Assault....A,Y,B,X while holding down the control pad left key. Than since you have limited time left to do this you press Y,X,X,B,Y,X,A,Y,B This gives you infinite