Single Mission :Ground
Recommended Units: Any with a good range weapon.
First part: Defend the Strike Gundam
Any unit works here. No shooting needed.
Second part: Destroy the Gundam Heads
It is highly recommended you use a unit with a good range, not like Shenlong Gundam, God Gundam's Hyper Mode, or units who have bad range or full on melee attacks. You need to shoot down the Gundam Heads in order to continue.
Third Part: Infiltrate the Enemy Base!
Any unit also works here but be evasive. A little into the base, there is a health box (Hard, Expert: It's hiding inside bigger boxes). Zaku II's will be swarming you, Zaku I's will come melee you, and Zaku III's will shoot you at long range.
Final Part: Destroy the Master Gundam (Hyper Mode)
For Easy: Pretty simple, just attack at him. There are Zaku I's and Zaku II's swarming around a little later and if you manage to destroy some of them, a health box will appear on the lower right hand corner of the room (from the way you entered, to your right). Melee as much as you want because this is the only difficulty where he will flinch.
For Normal, Hard, Expert: NEVER TRY TO MELEE HIM!!!! He is in Hyper Mode, and he can counterattack. Range is highly recommended on these 3 difficulties. He also does a spin attack which wil inflict Bullet Zero (I think).