Here is the full list of all 46 Army of TWO: The Devil's Cartel achievements worth 1,000 gamerscore.
Fully customize a weapon with 6 customizable parts or more
Complete Outside Contact
Kill 3 targets with 1 grenade
Players simultaneously killed 2 unaware targets
Level up to Rank 5
Complete Rally Point
Perform 10 cover to cover transition in a row
Perform 50 Hat Shots
Complete Cause and Effect
Make your first kill as a rookie (in Cause and Effect mission)
Complete New Blood
Complete Last Resort
Complete Salvation
Complete Enemy Territory
Complete Narco Hell
Complete Assault
Complete Confrontation
Complete the Campaign
Level up to Rank 15
Level up to Rank 25
200 targets killed in single Overkill (Triggered by you)
500 targets killed while in cover
200 targets killed in double Overkill
200 targets killed in single Overkill (Triggered by your partner)
100 targets killed using either an MMG or an MGL
Destroyed 500 objects
Buy All Guns
Buy All Outfits
Complete the game on Insane
Buy all Weapons, Tattoos, Masks and Outfits
Perform 250 Flank, Surprise and/or Tag Team kills
You took the Aggro for 100 Flank kills
Kill 10 Brutes in Physical Confrontation
Kill 3 targets or more using an explosive object in any level
Perform 100 Headshots
Perform 100 melee kills
Perform 50 Backstabs
You didn’t go wounded once in a mission (medium, hard or insane)
Perform a x10 Co-op Combo
Create your own Custom Mask
Apply the maximum number of layers on a customized mask
Destroy 50 cars
Headshot a target while blind firing
Perform a melee kill while you're in Overkill
Perform 10 melee kills on wounded targets
Complete a mission (excluding New Blood) with a human partner