Finish the single player campaign on any difficulty

Single Player: Kill 20 enemies with the Microwave cannon

Complete the evacuation at Times Square

Assist the evacuation at Bryant Park

Assist the Marines in Madison Square

Infiltrate the alien hive

Find Nathan Gould

Single Player: Kill at least 3 enemies with a single grenade

Single Player: Kill 4 enemies in a row with headshots

Don't kill any of the enemies that are on fire in Chapter 3: Fire Sale

Complete chapter 1 in the Single Player Campaign

Make it to the party as Mash.