(Online) Use Squad in the menu, find a friend and play one round

(Online) Reach Rank 8

(Online) Destroy 1000 walls

Kill 50 enemies with the AK-47

Kill 50 enemies with the SAS - 12

Finish the game in Easy Mode

Kill 20 enemies by shooting from the hip (without aiming with the L1 button)

Kill 30 enemies with the MP40

Kill 50 enemies with the 92FS - 9mm

Kill 20 enemies with the Wes - 44

Kill 100 enemies with headshots

Kill five enemies in a row with headshots