Successfully complete the game to unlock the "Big Heads" and "Infinite Ammo" cheats in the "Options" menu.

Prequel bonus - Have a saved game file from the original Army Of Two to unlock the AS-KRI and S0-Z Grand Pinger for purchase.

Bonus costumes - Successfully complete the game to unlock the Civilian, End, Light Armor, Mall, Medium Armor, and Old School costumes.

Start with fully upgraded weapons - Start a new game. Use the starting money to upgrade your weapons or buy new ones. Play the game until reaching the cutscene with the moral choice. Select the moral choice, then go to the main menu during the cutscene with the explosions. Select Campaign mode, and choose the one that was just played. Select "New", and you will have all the previously bought weapons, upgrades, and money from the previous mission. However, you can upgrade your weapons again. Repeat this process to fully upgrade and purchase all the starting weapons.

New areas - When entering a new area, take your time to explore it. There may be civilians around that you should protect or alternate paths that you and your partner can exploit.

Easy "Grenadier" achievement - At the first "Civilian" hostage spot in Chapter 1, tie down the three enemies, then throw a grenade in the middle of them to get the "Grenadier" achievement. Note: You will also kill the civilians with the grenade. Thus, restart from the checkpoint after getting the achievement.

Easy "Hate Monger" achievement - Upgrade a weapon until it has nearly a 100% aggro rating to get the "Hate Monger" achievement. Note: Style upgrades such as Jigsaw and Pimp will add a lot of aggro.

Easy "Pumpkin Patch" achievement - At the first "Civilian" hostage spot in Chapter 1, have your partner tie down the first enemy. The other two enemies will get on their knees, allowing you to shoot them both in the head with one bullet to get the "Pumpkin Patch" achievement. Note: Restart from the checkpoint after getting the achievement if desired.

Easy "Rock, Paper, Scissors" achievement - Press Y while not in combat and next to your partner to play rock, paper, scissors. Use the D-pad to select rock, paper, or scissors. Win three times in a row to get the "Rock, Paper, Scissors" achievement.

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Not What I Thought It Was (5 points): You need to complete Chapter 1 on Any Difficulty Level.
A Steep Descent (10 points): You need to complete Chapter 2 on Any Difficulty Level.
A Decent Animal (15 points): You need to complete Chapter 3 on Any Difficulty Level.
Emergency Room (20 points): You need to complete Chapter 4 on Any Difficulty Level.
Gone Shopping (25 points): You need to complete Chapter 5 on Any Difficulty Level.
Survivor? (30 points): You need to complete the Game on Any Difficulty Level.
Softcore (50 points): You need to complete Half the Game on Contractor Difficulty.
Hardcore (100 points): You need to complete the Game on Contractor Difficulty.
Meat Bag (15 points): You need to use 15 enemies as human shields.
Chaaaaarge! (15 points): You need to charge through 20 enemies.
The Beast (50 points): You need to kill 6,666 people in Campaign.
Grenadier (10 points): You need to kill 3 or more enemies with a single grenade.
Pistolier (20 points): You need to kill 150 enemies with a pistol.
Old Faithful (20 points): You need to kill 400 enemies with assault rifles, sub machineguns or shotguns.
One Shot, One Kill (20 points): You need to kill 100 enemies with a sniper rifle.
Quick Draw (15 points): You need to kill 25 enemies with a quick draw from mock surrender.
Open Hand Slap! (15 points): You need to kill 50 enemies with a melee or bayonet.
Unbreakable (25 points): You must survive an entire level in one session without being downed on normal difficulty or above.
Not So Bad After All (10 points): You need to tie up 15 enemy combatants instead of executing them.
Healer (10 points): You need to heal your partner 10 times.
Co-Op Sniper (10 points): You need to Co-Op Snipe 5 enemies.
Attention Grabber (10 points): You need to allow your partner to snipe 5 guys while in Mock Surrender.
In Synch (10 points): You need to kill two enemies with simultaneous Quick Draws while in Co-op Mock Surrender.
Pumpkin Patch (10 points): You need to shoot 2 enemies in the head with a single bullet.
Total FistBump Destruction (10 points): You need to finish the game as best friends.
Total Fistbump Deflation (10 points): You need to finish the game in a fractured friendship.
The Truth Is Right Here (20 points): You need to listen to all of the Radio Broadcasts.
Loot and Pillage (20 points): You need to collect $1,000,000.
Full Arsenal (30 points): You need to collect All Weapons and Weapon Parts.
Touch Not a Cat but a Glove (50 points): You need to shoot all Maneki Neko cats in the game.
Hate Monger (10 points): You need to customize a weapon to high aggro.
The Optimist (5 points): You need to make a positive coop morality choice.
The Pessimist (5 points): You need to make a negative coop morality choice.
Humanist (30 points): You need to save every hostage.

Additionally, there are sixteen secret achievements:

Rock, Paper, Scissors (5 points): Beat your partner at rock, paper, scissors three times in a row.
Fancy Meeting You Here (5 points): Versus: Invite a friend before joining a lobby to play a public match.
Job Seeker (10 points): Versus: In public matches, kill a player with the primary or secondary weapon from every weapon kit.
DIY PMC (10 points): Versus: Create a custom facemask online (www.armyoftwo.com) and wear it in a public match.
Death Dealer (10 points): Versus: Kill 10 players with headshots on a single map in a public match.
Power Couple (15 points): Versus: Earn the highest partnership score in a Co-op Deathmatch, Control or Warzone public match.
Future Visions (30 points): Unlock all Potential Futures.
All Guns Blazing (30 points): Versus: Kill a player with every weapon, including special weapons, in public matches.
Bound For Life (30 points): Versus: In a public match, survive an Extraction map without suffering a single death on your team.
Survival of the Fittest (50 points): Versus: Complete all 16 rounds of an Extraction game in a public match.
Big Game Hunting (5 points): Versus: Kill both members of a single partnership during a public match.
Fresh Meat (5 points): Versus: Revive your partner and perform a partner reload during the same public match.
Scavenger (15 points): Build a gun using 3 homebrew parts.
Heartless (20 points): Make only negative choices.
Purist (20 points): Make only positive choices.
King of the Hill (30 points): Versus: Win a public match on every map in Co-op Deathmatch, Control and Warzone.