Zombie Hunter: Defeat at least 1,000 zombies.
Zombie Killer: Defeat at least 10,000 zombies.
Zombie Genocider: Defeat at least 53,594 zombies.
Self Defense: Defeat at least 1 psychopath.
Peace Keeper: Defeat at least 5 psychopaths.
Punisher: Defeat at least 10 psychopaths.
Legendary Soldier: Unknown
Hella Copter: Unknown
Tour Guide: Escort 8 survivors at once.
Frank the Pimp: Simultaneously escort 8 female survivors.
Full Set: Collect all portraits in the notebook.
Humanist: Get at least 10 survivors out of the mall.
Life Saver: Get at least 20 survivors out of the mall.
Saint: Get at least 50 survivors out of the mall.
Strike!: Send at least 10 zombies flying with bowling balls.
Costume Party: Place novelty masks on at least 10 zombies.
Raining Zombies: Knock at least 30 zombies aside with a parasol.
Gourmet: Eat all types of food available in the mall.
Item Smasher: Break at least 100 items.
Bullet Point: Fire at least 1,000 bullets.
Perfect Gunner: Don't miss with a machine gun.
Photojournalist: Score at least 1,500 PP from a single photo.
The Artiste: Score at least 3,000 PP from a single photo.
Group Photo: Get 50 Target Markers with the camera.
Portraiture: Photograph at least 10 survivors.
Census Taker: Photograph at least 50 survivors.
Psycho Photo: Photograph at least 4 psychopaths.
Psycho Collector: Photograph at least 10 psychopaths.
PP Collector: Photograph all PP Stickers.
Snuff Shot B: Unknown
Snuff Shot J: Unknown
Transmissionary: Answer all calls from Otis.
Indoorsman: Spend at least 24 hours indoors.
Outdoorsman: Spend at least 24 hours outdoors.
Freefall: Drop from a height of at least 16 feet (5 meters).
Marathon Runner: Cover a distance of 26.2 miles (42.195 km).
Carjacker: Steal the convicts' vehicle.
Stunt Driver: Jump a car at least 33 feet (10 meters).
Stunt Rider: Jump a motorcycle at least 33 feet (10 meters).
Zombie Road: Walk over 33 feet (10 meters) on the backs of zombies using the Zombie Ride.
Karate Champ: Defeat at least 1,000 zombies barehanded.
Sharp Dresser: Change into at least 20 different costumes.
Clothes Horse: Change into all costumes available in the mall.
Level Max: Reach level 50.
Unbreakable: Get the true ending without being knocked out.
Overtime Mode: Unveil all cases and be at the heliport at noon.
8 Mode: Get the true ending.
3 Day Survivor: Survive for at least 72 hours.
5 Day Survivor: Survive for at least 5 days.
7 Day Survivor: Survive for at least 7 days.

Ending requirements - These are the requirements needed in 72 hour mode to unlock different ending the farther in the letter goes the worst it is i.e. f=worst a= best

Unlockables
Ending A Solve all cases, talk to Isabella at 10am, and return to the heleport at 12 pm on the 22nd
Ending B Don't solve all cases and be at the heliport on time
Ending C Solve all cases but do not talk to Isabella at 10am on the last day
Ending D Be a prisoner of the special forces at 12 pm on the 22nd
Ending E Dont be at the helliport and dont solve all cases
Ending F Fail to collect all of Carlitos bombs on act 7-2

Unlock Weapon: Molotov Cocktail  -  You can obtain the Molotov Cocktail that one of the Boss, Paul uses:

1) After the boss fight, when Paul is on fire, DO NOT KILL him. Instead, pick up the fire extinguisher in the store to put out the fire.

2) Then bring Paul back to the security room. (You can also save the 2 women as well)

3) After a while, you will receive a call saying Paul has a present for you,

4) Go back to the security room to meet Paul, continue to talk to him and he will give you his Molotov Cocktail to use. (Unlimited supply!)

Unlockables

Molotov Cocktail (infinite supply) Use fire Extinguisher to save Paul, then bring him to the security room.

A handful of the Achievements have Unlockable content that becomes available once they've been activated. These, rewards, which include special costumes and items, can be found inside Shopping Bags behind the air duct in the Security Room.

Ammo Belt Perfect Gunner
Arthur's Boxers 7 Day Survivor
Cop Hat Saint
Hockey Mask PP Collector
Laser Sword 5 Day Survivor
Mall Employee Uniform Transmissionary
Mega Man Boots Unbreakable
Mega Man Tights Punisher
Prisoner Garb Carjacker
Pro Wrestling Boots Item Smasher
Pro Wrestling Briefs Karate Champ
Real Mega Buster. Zombie Genocide
Special Forces Boots Legendary Soldier
Special Forces Uniform Hella Copter
White Hat Census Taker

Infinity Mode This is unlocked by completing Overtime Mode
Overtime Mode Complete all missions in 72 mode, talk to Isabella at 10am, and return to the helipad by noon on the 22nd