Tip #1: Unlock overtime mode. You have to complete all case missions up to The Facts and talk to Isabela in Carlito's hideout before and after the 10 a.m. cutscene. After you do that, go back to the helipad by 12:00 p.m. on the 22nd.
Tip #2: Unlock infinity mode. Now you have to complete Overtime mode and get the "True Ending". Note that in that mode you lose 1 life bar per 100 seconds. You need 20 real minutes to lose all 12 life bars.
Tip #3: One hit kill weapon. In the Paradise Plaza get to the second floor and find the Colombian Roastmasters in the food court. Then find an orange platform on the rail, jump on it and get katana, one of the most powerful weapons in the game.
Tip #4: Unlock Shotgun. Go to the Entrance Plaza for the first time. One of the men talking near the entrance has a shotgun. Actually, you have to run up to his body when zombies attack you. Get the shotgun and run upstairs. Use this weapon to defeat bosses.
Tip #5: Unlock trip attack. Press X while jumping right when your feet are just off the ground. If you trip zombies with your spinning leg, you will get 30 PP for each one you hit.
Tip #6: Unlock easy zombie kills. While in Leisure Park, go to the parking garage and get in the car which is outside. Now you should drive down into the parking garage and run over zombies until you get to another vehicle. hen you should switch it and return. Thus you will receive a respawned car. Not that it's possible to repeat this cheat.
Tip #7: Get back regular outfit. Go to the janitor's room, underneath the stairs leading to the heliport to set default outfit if you don't like one you have.
Now, complete the folllowing tasks to unlock bonuses:
Arthur's Boxers: Survive for 7 days.
Laser Sword: Survive for 5 days.
Mall Employee Uniform: answer all calls from Otis.
Mega Man Boots: get the true ending without being knocked out.
Mega Man Tights: defeat 10 psychopaths.
Prisoner Garb: steal the convicts' vehicle.
Pro Wrestling Boots: break 100 items.
Pro Wrestling Briefs: defeat 1,000 zombies barehanded.
Real Mega Buster: defeat 53,594 zombies.
Special Forces Boots: defeat 15 psychopaths or 10 special forces soldiers.
Unknown: get 50 survivors out of the mall.