After beating the game, or at least a level, you'll notice that you'll have a total of five unlockable cheats when attempting to replay a level via the "level select" option. Here's how to unlock them.
Bullet Cam on Every Kill - Find every clue.
One-Hit Kill - Beat game on Hardcore with Free Aim.
Unlimited Ammo - Collect all golden gun pieces.
Unlimited BulletTime - Earn a gold-medal score (about 7,000) or better on every level in arcade mode.
Unlimited Pain Killers - Beat game on Hard with Free Aim.
Play the Piano
In Chapter 1, Max can play the piano in the first apartment.
In Chapters 3 and 4, there are TVs throughout the game that show special programs when turned on.
Baby Crying from Max Payne 1 Dream
In the soundtrack of Chapter 8, you can hear the baby crying from the dream sequences of Max Payne 1 in the background.
Finishing the Game on Any Difficulty
Unlock New York Minute mode in Arcade Mode
Finishing the Game on Medium
Unlock Character Select Option in Arcade Mode
Finishing the Game on Hard
Unlock Old School Difficulty
Unlock Hardcore Difficulty
Unlock Unlimited Painkillers Cheat
Finishing the Game on Old School
Unlock Max Payne Advanced Character Model
Finishing the Game on Hardcore
Unlock One Hit Kill Cheat
Deathmatch Made In Heaven Mode Pack Trophies
There are 5 Bronze Trophies and 2 Silver Trophies.
Painful Memories DLC Trophies
3 Blind Mice (Bronze) - Blind 3 players simultaneously with the Pepper Spray
Betty Confetti (Bronze) - Kill a player with the Bouncing Betty
Breaking and Entering (Silver) - Open 15 Containers or Doors in a single game of Dead Men Walking
Breaking the 4th (Bronze) - Earn a x4 multiplier in Challenge Mode
It Looked Easy Enough (Silver) - Complete the Challenge Mode
Resisting Arrest (Bronze) - Stun 10 players with either the cattle prod or stun gun
Sweaty Betty (Bronze) - Trigger and avoid a Bouncing Betty by Shootdodging
There are 5 Silver Trophies.
Long Arm of the Lawless Kill Max Payne in Panama as the De Marcos
Bar Brawler Kill someone with a melee strike in the Bar area of Hoboken Bar
Ouch My Head Headshot someone with a Hangover
Welcome Ashore Kill a player on the yacht from the observation platform of the Panama Canal
Drinker's Revenge Kill the sniper who broke your Hip Flask in the same life
Hostage Negotiation Map Pack Trophies
There are 1 Bronze Trophy, 3 Silver Trophies.
60 Seconds of Intimidation (Silver) - Grind 60 Seconds of Intimidation on enemy players
Early Adopter (Silver) - In a single game, kill the same player with both the M24 and the IA2 AR
Old School Moves (Bronze) - Perform a 720 spin while prone in Nightclub
WMD (Silver) - Get 3 kills from a single use of the level 3 explosives burst
Local Justice Map Pack Trophies
There are 4 Bronze Trophies and 1 Gold Trophy.
Air Ace (Bronze) - Get 2 kills in a single Shootdodge in the Departure Lounge
Express Checkout (Bronze) - Kill 4 players within 3 seconds in the Imperial Palace
Keep Your Nose Clean (Gold) - Get 100 Kills as a member of the SPP
Long Arm of the Law (Bronze) - Win 20 Vendettas in the 55th Battalion HQ
M4 Murder (Bronze) - Level up your M4 Assault all the way to level 10
Feel the Payne – Story Complete [MEDIUM]
Serious Payne – Story Complete [HARD]
Maximum Payne – Story Complete [OLD SCHOOL]
Payne In The Ass – Story Complete [HARDCORE]
It’s Fear That Gives Men Wings – 10 Bullet Time® Kills In A Row
You Could Hurt Somebody With That – Shoot 10 Airborne Grenades
You Sure Know How To Pick A Place – Discover All Tourist Locations
The Fear Of Losing It – Survive A Level Without Painkillers
One Bullet At A Time – 300 Headshots
You Play, You Pay, You Bastard – 100 Kills With Melee
With Practiced Bravado – 100 Kills During Shootdodge
Past The Point Of No Return – Take 100 Painkillers
A Few Hundred Bullets Back – Use Every Weapon In The Game
Colder Than The Devil’s Heart – Kill 30 Enemies In 2 Minutes
Part I Complete – Complete Part I Of The Story
Part II Complete – Complete Part II Of The Story
Part III Complete – Complete Part III Of The Story
Out The Window – Get 6 Kills While Diving Through The VIP Window [FREE AIM]
The One Eyed Man Is King – Cover Passos With Perfect Aim
That Old Familiar Feeling – Clear The Hallway Of Lasers
Something Wicked This Way Comes – Get 7 Kills While Jumping From The Rickety Boat [FREE AIM]
Amidst The Wreckage – Destroy All The Models In The Boardroom
So Much For Being Subtle – Get 9 Kills While Being Pulled By A Chain [FREE AIM]
The Shadows Rushed Me – Unlock And Complete New York Minute Hardcore
The Only Choice Given – Get 8 Kills While Dangling From A Chain [FREE AIM]
Along For The Ride – Trigger A Bullet Cam On The Zipline [FREE AIM]
Sometimes You Get Lucky – Get A Headshot During The Rooftop Tremors
It Was Chaos And Luck – Get 6 Kills While Riding The Push Cart [FREE AIM]
The Road-Kill Behind Me – Total Everything On The Runway
Trouble Had Come To Me – Clear Everyone On The Bus Ride
All Of The Above – Finish All Grinds
An Echo Of The Past – Find All Clues
A License To Kill – Collect All Golden Guns
A New York Minute – Finish In A New York Minute
Full Monty – Complete One Of Each Game Mode Including All Gang Wars
Payne Bringer – Kill 100 Other Players
Max Payne Invitational – You Invited Someone To Play
Man Of Many Weapons – Unlock All Weapons
Man Of Many Faces – Unlock All Faction Characters
Deathmatch Challenge – Winner In Any Deathmatch
Grave Robber – Looted A Body
The Gambler – Won A Wager
Training Complete – Achieve Level Rank 50
Dearest Of All My Friends – Kill Someone On Your Friends List