Genocide Gun:
Complete all missions under the Inferno difficulty setting.
PX50 Bound Shot:
Complete all missions under the Hardest difficulty setting.
Y20 Impulse:
Complete all missions under the Hard difficulty setting.
ZE Launcher:
Complete all missions under the Normal difficulty setting.
Zero Laser Rifle:
Complete all missions under the Easy difficulty setting.
Mission 13: Easy completion
Walk to the water and swim. Let all the ants gather around you. Eventually you can walk on top of them and they cannot attack you. Just run around and shoot at your feet and they will eventually die. You can do this on the Inferno difficulty setting and get the mega powered weapons early.Mission 25: Easy completion
To do this, bring a weapon of your choice and C70. It starts appearing on the Hardest difficulty around level 36; try farming level 40 on Hardest). As soon as the level begins, start dropping C70 off the sides of the path and detonating them. Remember that the C70 has a 40 meter blast radius; be careful not to be in it. You should be able to get the enemy numbers down to about 20 by doing this. Then, just mop up the remnants. Note: This also works on Infiltration 1. Achievements:
Complete the following achievements to unlock Xbox Live Gamerscore points.
All Stages Cleared - Easy (50 points): Acquired after clearing all stages in Easy mode.
All Stages Cleared - Normal (100 points): Acquired after clearing all stages in Normal mode.
All Stages Cleared - Hard (150 points): Acquired after clearing all stages in Hard mode.
All Stages Cleared - Hardest (200 points): Acquired after clearing all stages in Hardest mode.
All Stages Cleared - Inferno (300 points): Acquired after clearing all stages in Inferno mode.
All Weapons Acquired (200 points): Awarded after acquiring all the weapons in the game | 
