Here is the full list of all 100 Major Mayhem achievements.
Finish Metropolis in Survival mode
Defeat 2,000 enemies with the Automatic Shotgun
Defeat 2,000 enemies with the Grenade Launcher
Defeat 2,000 enemies with the Auto Launcher
Score 250,000 points in Arcade mode
Defeat 2,000 enemies with the P99
Spend 100,000 coins in the Armory
Play 25 arcade games
Defeat 2,000 enemies with the Minigun
Score 150,000 points in Arcade mode
Defeat 2,000 enemies with the Sniper Rifle
Defeat 2,000 enemies with the Bazooka
Unlock all the clothing items in the Armory
Defeat 2,000 enemies with a silenced weapon
Defeat 2,000 enemies with the Rifle
Defeat 2,000 enemies with the Shotgun
Rescue 1,000 hostages
Defeat 2,000 enemies with the Uzi
Defeat 2,000 enemies with the Automatic Sniper Rifle
Defeat 500 enemies with a Chicken Cannon
Defeat 500 enemies with the Grenade Launcher
Defeat 2,000 enemies with the Pistol
Defeat 500 enemies with Grenades
Defeat 2,000 enemies with the Plasma Rifle
Finish the Tropics in Survival mode
Shoot 1,000 chickens
Defeat 2,000 enemies with the Magnum
Defeat 2,000 enemies with the Quadzooka
Score 50,000 points in Timebomb mode
Rescue 5 hostages in a single Timebomb game
Defeat 100 enemy tanks
Use 5 or more weapons in one Timebomb game
Rescue 100 hostages in a row
Score 20,000 points in Timebomb mode
Score 50,000 points in Arcade mode
Complete all the 150 mission objectives
Defeat 2,000 enemies with the Light Machine Gun
Use the Chicken Cannon and wear the chicken hat as the General
Unlock all the weapons in the Armory
Defeat 500 enemies with the Quadzooka
Defeat 500 enemies with the Plasma Rifle
Trigger 100 barrel chain reactions
Shoot down 100 enemy jets
Remove 1,000 hats from enemies that are already dead
Defeat 500 enemies with the Automatic Sniper Rifle
Defeat 500 enemies with the Minigun
Get 1,000 Close shaves
Defeat 500 enemies with the Automatic Shotgun
Earn a multiplier of x100
Defeat all the red bonus ninjas
Run 50 kilometers
Defeat 10,000 enemies
Hit an enemy with every shot in a mission
Perform 100 dive rolls
Defeat 500 enemies with the Light Machine Gun
Use the Light Machine Gun and wear the red bandana as Rambro
Shoot 30 chickens in a single Arcade game
Defeat 500 enemies with a silenced weapon
Defeat 500 enemies with the Rifle
Completely dismantle the Giant Death Machine
Collect 10,000 coins
Shoot 4 chickens simultaneously
Discover all the multiplier call outs
Defeat 500 enemies with the Bazooka
Defeat 500 enemies with the Magnum
Check out our Twitter feed or Facebook page
Use the Silenced Pistol while wearing the Tuxedo
Have 10,000 coins in the bank
Defeat 1,000 enemies shirtless
Defeat the end boss (Classic or Survival mode)
Play Major Mayhem on 3 consecutive days
Defeat 500 enemies with the P99
Defeat 4 enemies simultaneously
Defeat 100 enemies with barrel explosions
Play in all 3 locations during a single Arcade game
Get 100 double kills with the Shotgun
Defeat 500 enemies with the Pistol
Defeat 500 enemies with the Sniper Rifle
Play Major Mayhem for 2 hours
Defeat 100 enemies by shooting through an object
Purchase one of each of the 5 power ups
Defeat 500 enemies with the Shotgun
Jump 20 times in one mission
Defeat 500 enemies with the Uzi
Unlock all the game modes
Defeat 1,000 enemies
Complete all the other achievements
Defeat 50,000 enemies
Remove 10,000 enemy hats
Deflect 1,000 projectiles
Finish the Desert in Survival mode
Complete all the missions in a row without dying (Classic or Survival mode)
Earn 3 medals on all Tropic missions in Classic mode
Earn 3 medals on all Metropolis missions in Classic mode
Earn 3 medals on all Desert missions in Classic mode
Play 100 Timebomb games
Score 100,000 points in Timebomb mode
Defeat 2,000 enemies with a Chicken Cannon
Defeat 2,000 enemies with Grenades