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God mode is when you have Infinite health (You can't die) This can be done in two ways: Setting your health to -1 or a VERY high number.
But setting it to -1 causes a bloody screen though. It could be fixed but idk how.
This can be done on a PS3... For SP....for multiplayer you'd have to be host but since I dont use MW3 on the PS3 im not the right guy to ask about it. For one you'd need CFW (Or at least a sort of jailbreak so u can install .pkgs to get a look at MW3's internals)
And auto quick scope, that is just an aimbot that has the ability to zoom in-out quickly to make it look like a quickscope.