Beat the game on the hardest difficulty. Then then during a new game pause and hit left left right Y.
Extra options menu  -  Beat the game on any difficult setting and you will find extra things like Beam spray-Gun

HI-Power generator

Photo1
Proto Beam Rifle

Photo2
Lunar Titanium

Beam Rifle

Hit enemy mobile suits from behind. When the fall down ,pound on them with every thing you have.

Unless you have to rush, scope out the map slowly, scanning the horizon constantly. That way you can catch sight of targets, usually before they see you.

Using your Suit-mates is an integral part of the game's strategy. If you're fighting multiple targets, switch to the map and order the other Suits to take them out, so that you aren't mobbed.

Another good strategy with your squad is to order one to fight at close range, another at medium, while you hang back and use your sniper mode to fight long range.

Remember that you can blow limbs off the other Suits. Thus, if you blow away the gun arm of an enemy, he can't use that weapon anymore (and will often retreat).

Bonus Option  -  After completing the game on any difficulty setting and saving it, a new option will appear on the Main Menu.                   

Level 1

Unlimited Armor:  80F396D700000384 
Unlimited Primary Ammo:  49DA041F0000001C 
Unlimited Special Ammo:  7E25C8D40000001C 
Low Heat:  B7B6215B00000000 
Low Barrel Heat:  7E1DC8D400000000

Level 2 

Unlimited Armor:  15A4305D00000384 
Unlimited Primary Ammo:  EF773E580000000A 
Unlimited Special Ammo:  2FE745890000000A 
Low Heat:  85A3ABCC00000000 
Low Barrel Heat:  2FDF458900000000