At the custom character screen, press Y, then enter "phayder" as a code to unlock Alanna (Necris).
At the custom character screen, press Y, then enter "jihan" as a code to unlock Ariel (Iron Clad).
Successfully complete the indicated task to unlock the corresponding character:
Lauren: Always select the second choice for all missions. Kill Lauren in Deathmatch in Chapter 2 of Campaign mode. Lauren will eventually become unlocked after a subsequent Deathmatch in that chapter.
Scythe: Always select the second choice for all missions. Kill Scythe in Deathmatch in Chapter 4 of Campaign mode. Scythe will eventually become unlocked after a subsequent Deathmatch in that chapter.
Matrix: Always select the second choice for all missions. Kill Matrix in Deathmatch in Chapter 3 of Campaign mode. Matrix will become unlocked after a side mission in Chapter 3 in that chapter.
Akasha: Kill Akasha in the final mission.
Loque: Unlocked after a Capture The Flag match in Chapter 5.
Damian: Unlocked in Chapter 4 of Campagin mode.
Kragoth: Unlocked in Chapter 4 of Campagin mode.
Malakai: Unlocked in Chapter 4 of Campagin mode.
In the "Heatray" level in Multiplayer Deathmatch mode, after the Dark Walker drops, destroy it to get a Damage Amplification.
There are orange and green looking energy/grainy appearing walls that you can walk through as well as shoot through. There are two of these orange walls that are circular in shape at the top of the map that allows you to reach a sniper rifle.
Use the following trick to talk with your headset more effectively instead of holding D-pad Right. Hold D-pad Right, unplug your headset, reinsert your headset, then release D-pad Right. If done correctly, the microphone symbol should stay on screen, and you no longer have to hold D-Pad Right to talk.
Accomplish the indicated achievement to get the corresponding number of Gamerscore points: