To get the following bonuses in the game complete ALL the missions in the indicated difficulty setting.

Unlock Zero Laser Rifle:
Complete ALL the missions on the Easy difficulty setting.

Unlock ZE Launcher:
Complete ALL the missions on the Normal difficulty setting.

Unlock Y20 Impulse:
Complete ALL the missions on the Hard difficulty setting.

Unlock PX50 Bound Shot:
Complete ALL the missions on the Hardest difficulty setting.

Unlock Genocide Gun:
Complete ALL the missions on the Inferno difficulty setting.

Complete the following tasks to get the alloted GamerScore Points:

All Stages Cleared - Easy - GamerScore 50:
Clear ALL stages in Easy mode.

All Stages Cleared - Normal - GamerScore 100:
Clear ALL stages in Normal mode.

All Stages Cleared - Hard - GamerScore 150:
Clear ALL stages in Hard mode.

All Stages Cleared - Hardest - GamerScore 200:
Clear ALL stages in Hardest mode.

All Stages Cleared - Inferno - GamerScore 300:
Clear ALL stages in Inferno mode.

All Weapons Acquired - GamerScore 200:
Get ALL the weapons in the game.

The following weapons are unlocked by completing ALL the missions on the corresponding difficulty.

Unlock Zero Laser Rifle:
Beat ALL the missions on 'Easy' difficulty setting.

Unlock ZE Launcher:
Beat ALL the missions on 'Normal' difficulty setting.

Unlock Y20 Impulse:
Beat ALL the missions on 'Hard' difficulty setting.

Unlock PX50 Bound Shot:
Beat ALL the missions on 'Hardest' difficulty setting.

Unlock Genocide Gun:
Beat ALL the missions on Inferno difficulty setting.