License plates  -  Look at the license plates of cars in different levels. In the "A New Life" mission, the license plate of all the cars reads BADBLOD (Bad Blood). In the "A House Of Cards" mission, the license plate of the first limo at the casino reads "L1MONEY", or something similar.

Newspaper headlines  -  After completing a mission, the newspaper headline will vary depending on how you did. If you did poorly, the paper will say so in the paragraph. If you shoot very little and use mostly hand to hand it will say that there is not enough information to make a ranked description of you. If you completed the mission with high accuracy, it will state that you are a well trained marksman. Try completing missions differently to see different headlines.

Alternate ending sequence  -  In the final level "Requiem", Diana will give you the antidote to the death serum. You will fade in and out of life (power bar rises and drops to the beat of Agent 47's heart) while the credits roll. If you do nothing, the game will end. However, if you press the Left Analog-stick Up and Down (or any other buttons) repeatedly, you will come back to life and your mission will be to leave no witnesses.

Easy "Silent Assassin" rank in A New Life mission  -  Start the mission with no weapons except for your standard equipment. First, go to the back of the food truck when the delivery man is walking off. Pick up the donuts, then take them around the corner so that nobody can see you. Put them on the floor and then scroll through your inventory. Select the "Sedative Syringe", then look down at the donut box and inject the sedative into them. Pick up the donuts again, put the syringe away, then go back to the food truck. Drop the box of donuts on the floor directly behind it, then walk away. The delivery man will pick up the donuts and take them to the FBI van across the road. Wait a short time and an short intermission sequence inside the truck will appear, showing the FBI agents falling asleep. Go to the back of the truck, open the door when prompted, and go inside. When inside the FBI truck, suit up as an FBI agent, and steal the video tape, which should be on the left side of the van as you go in. Do not pick up any weapons. Leave the vehicle and go up to the front of the house and walk inside. Go out the back towards the shed, which is in the top right hand corner. Wait until there is nobody around. If the pool man goes in, do not try to follow him or your suspicion bar will go into the yellow. When there is nobody around, pick the lock, go inside, and pick up the lighter fluid. Exit the shed, go right, and then go towards the pool. Over to your right is a barbecue. Go up to it and you will get the "Rig the Barbeque" option. Select it, then go inside the house and wait under the stairs. Stand around for a short time and a short intermission sequence will show a woman being burned alive. When she is dead, go back outside and pick up the microfilm that she is wearing around her neck. Go back inside, then go up the stairs. Turn right across the landing, then go straight. Open the first door on your right, then go in and wait behind the L-shaped wall. If the main target is already there, wait for him to leave, then wait awhile for him to return. When he returns, make sure he has his back towards you, then fibrewire him. When he dies, drag his body to the place you were hiding (the L-shaped wall). Then, sprint out of the house towards your escape as quickly as possible. If done in a short time, you should get either a "Hitman" rating or "Silent Assassin" rank. Either way, you will get $100,000 and if you have already completed the game you can purchase an additional upgrade to your custom weapons whenever you select a mission.

Easy "Special Rating" achievement in A New Life mission  -  You will need a minimum of ten headshots for this achievement as well as a silenced sniper rifle, and the foil case. In the A New Life mission, select your sniper rifle as your only weapon. Walk around to the tree house at the end of the street where you find the air rifle. It is at the exclamation point near the ladder in the middle of the map. Unpack your rifle and snipe every FBI agent that gets within your sights. Shortly afterwards, two cars will arrive carrying more agents. Snipe these as well, making sure not to hit any civilians or the dog. You should end up with two guards remaining in the surveillance van out front, one at the front door, and one at the back door. Pack your sniper into the foil case and walk back to the surveillance van, but turn into the open garage on the left. Unpack and assemble the rifle in the back corner, dropping the rifle on the floor of the garage. Walk to the other side of the street and poison the donuts when no one is looking. Wait for the caterer to deliver the donuts and watch the intermission sequence. Enter the van when the jogger is out of sight. Change into an FBI suit and use the phone to call the witness. Leave the van immediately and pick up your rifle. Snipe the guard at the front door and look to the left. You should see the witness on the phone in the living room window; snipe him as well. Enter the house through the door to the left of the garage. Walk north to the bedroom with the open window and climb out. Walk to the back corner of the yard and snipe the final FBI agent at the back door. Pack your sniper rifle up and enter the window again. Leave the case in the bedroom and get your sedative syringe ready. Find the wife of the witness running anxiously through the house and sedate her to take the microfilm necklace. Pickup your sniper case on the way out. Change back into your suit you left in the surveillance van, then proceed to the exit to gain the achievement and read an interesting headline.

Secret "Slugger" rank in A New Life mission  -  Kill everyone in the mission, even the dog, with the baseball bat to get the "Slugger" special rank.

Quickly get FBI clothes in A New Life mission  -  Normally to get the FBI clothes, you would drug the donuts and feed them to the feds in the van. You would then see them get sick and pass out before entering the van again. You do not actually have to do this. As soon as you see them getting sick, you can enter the van. They will be so sick, they will not notice.

Body bag in A New Life mission  -  At the beginning of the mission, stick your mine in the catering case. The man will carry it out back later. When he is in the back, blow the case. The agents will crowd around and one will say "Damn, not another one. I hate having to do this." or something similar. He will then put the man in a body bag and drag him into another room.

Easy "Silent Assassin" rank in A Vintage Year mission  -  You do not need any weapons for this mission; you only need the Anti Personnel Mine, Sedative Serum, and Coins. At the start of the mission, do not follow the tourists. Instead, go west along the outer wall. When you get to the corner you will see a broken truck. Check your map for guards. There should be one south of your location. Go around him using trees and bushes as your cover. You do not need to crawl, as he usually does not notice if you are a fair distance away. Once you pass him use the serum and sedate him from the back. Take his clothes and leave him there. Get in the rear compartment of the broken truck then get on its roof. From there, get on the storage room roof. Slowly crawl through there to the hole in the roof then jump in. The other guards will not pay much attention to you since you are wearing the guard's clothes. You do not need to worry about the alert level, even if it rises. Run out of the storage facility and across the square. Go to the right from the mansion and through the wooden door. Keep running straight and take the first door to the left that leads to the basement. You should see a guard as soon as you open the door. Place a mine next to him on the gadget with rope. Check the map until you notice a red blip (the target) enter a small square opening below you. As soon as this happens, get a few yards back from the explosive. Throw a coin on the ground so the guard comes to it. Detonate the mine once guard clears off. By doing this, the guard will not die and you will not suffer a penalty for an unnecessary kill. Wait for some guards to run to the place you are at, then make your way back to the mansion. Instead of the front entrance, use the small door on the left of it. This will lead you just a bit underground. Go to the door on the right and wait (with your map on) for the guard who is parallel to you to come by and turn around (starts marching back). Open the door, go to him and sedate him. Drag the guard to the nearest room to your right and take his clothes. He is a different type of guard who can move around the house freely. Dressed as a VIP guard, go to second floor and into the room with your target. Do not bother to crawl. Go to the balcony and throw a few coins on the ground to get his attention. Once he comes to check it out, get behind him and push him over the rail. Both targets are now dead. Check your map. There should be a "!" mark nearby, which is a window. Get out of it and down the roof. Get off the roof and go right behind the corner. There will be a narrow passageway down to the plane. Notice this is the place where the second target has landed. Do not forget to pick up his weapon on your way down. When you are near the plane, crawl by the one worker and two guards that are nearby. Ignore the worker and walk around the path. Get into the plane and complete the mission.

Play piano in A Vintage Year mission  -  To play the piano, walk up to it and shoot it in different locations to make different sounds.

Keep custom weapons in Amendment XXV mission  -  There are two methods to take weapons such as the Silverballers, etc. through the White House and bypass the metal detectors. The first method is to go to the other end of the parking lot when you start. Look to the left when you get to the end and you should see a ICA storage box. Put your custom weapons in it, then go into the White House through the double doors at the front and walk through the metal detectors. Remember that fibre wire, syringes, mines, and the detonator will not activate metal detectors. Go to the other end of the lobby. There should be a guard behind a rope watching some double doors. Go into the door on his left (the toilet), and stand facing the corner furthest away from the door and the toilet. Wait for the museum member or staff to walk in and for the door to shut behind him. Take out a silent weapon (fibre wire or syringe) and use it on him before he opens the door. Take his clothes and hide him as best as possible against the corner furthest from the toilet, but closest to the door. Check the map. If there is an innocent person in the lobby looking in your direction, wait for him to start walking away before opening the door or he will see the body and you will be shot. Open the door when you get the chance. While staying behind the ropes, walk across the width of the lobby and through the door on the other side. Go directly to the other end of the next corridor and take the last door on the left. This should lead you outside. When you get the chance to take out the U.S. Marine who patrols here, do so then hide him behind the big steel block. Take his clothes and gun. Walk back out the front doors and you should beep when going through the scanner, but the guards will not shoot you. Take your weapons out of the storage box from the side of the building and conceal them. When you go back in you should beep, but once again the guards should ignore it as long as you have your M14 at the ready.

Dancing Agent 47 in The Murder Of Crows mission  -  Get one of the disguises for the Salsa, Rock, or Blues bar. Then, move Agent 47 on the dance floor and allow the game to idle. After a few minutes, he will begin to dance. Note: If you move him around while he is dancing, he will stop; however, you can still move the camera around while he dancing.

Easy "Silent Assassin" rank in Curtains Down mission  -  This trick requires that you have the scope for your Silverballer. When the mission begins, run up the steps and to the right. Toss a bomb and quickly pick the lock on the first door on the left. Walk in and explode the bomb. Wait a moment, then snipe the man up in his private box and the actor walking on stage. Put your gun away and get out of there. If done correctly, you will get a "Silent Assassin" rank in under a minute.

For the second method, do the same as above, but when the Marine is out of the way, do not take his clothes or his gun. Work your way back out the front doors and go to the storage box. Take out a weapon and hold the weapon so you can throw it. Aim up and past the fence, towards the White House wall. Bounce your weapon off the wall and it will land on the other side of the fence. Do this with all your weapons, then go back to the area where you incapacitated the Marine. Walk down the alley and pick up your guns, then conceal them. Make sure you are far enough behind the wall for the guards out the front not to see you or they will shoot at you. Note: This method is useful if the game glitches and the Marines shoot at you even when you look like one.

Get police clothes in Flatline mission  -  As soon as the mission starts, you will see a guard shack. Run to the side door and enter. The cop inside will tell you to leave. Leave, then wait a moment and walk back in. He will be walking the other way and will not see you. Quickly sedate or kill him. Take his gun and clothes. Also, check the gun box next to the door for extra ammunition.

The Simpsons reference  -  In The Murder Of Crows mission, kill at least one police officer. At the end of the mission, the newspaper article will read "Police intend to put a low priority on investigating the deaths of the security officials. NOPD chief Wiggum states, 'The deaths of our fellow officers were tragic. We will find out who killed them.'", or something similar. -From: shadowofthereal1

Weapons

Pistols

Bull.480
Desert Eagle
Silverballer
Slp.40 Pistol
Snub Nosed
Six Shooter
Slp.40s

Shotguns

Shotgun
SP12 Shotgun

SMGs

MP5
MP7
MP9
SAF SMG
SMG tactical
TMP

Rifles

Air Rifle
FN-2000
M4
M14
SG552

Sniper rifles

Dragunov
Elephant Rifle
Kazo Trg
W2000 Sniper

No hideout weapons

Nailer

Upgrades

M4

Ris handguard ($50,000)
Low velocity ammo ($50,000)
Butt stock ($50,000)
Extra ammo ($75,000)
Laser sight ($75,000)
Rail mount ($75,000)
Armor piercing bullets ($75,000)
Silencer type 1 ($100,000)
Pistol grip ($100,000)
Double clip ($150,000)
Red dot sight ($150,000)
Silencer type 2 ($200,000)
Drum magazine ($200,000)
Scope type 1 ($200,000)

Silverballer

Low velocity ammo ($50,000)
Silencer type 1 ($50,000)
Extra ammo ($75,000)
Laser sight ($75,000)
Rail mount ($75,000)
Magnum ammo ($100,000)
Dual action ($100,000)
Long slide ($100,000)
Red dot sight ($150,000)
Large clip ($150,000)
Silencer type 2 ($200,000)
Full auto fire ($200,000)
Scope type 1 ($200,000)

SMG Tactical

Butt stock ($50,000)
Low velocity ammo ($50,000)
Extra ammo ($75,000)
Rail mount ($75,000)
Magnum ammo ($75,000)
Rapid fire ($100,000)
Short barrel ($100,000)
Silencertype 1 ($100,000)
Laser sight ($150,000)
Double clip ($150,000)
Silencer type 2 ($200,000)
Red dot sight ($200,000)

SP12 Shotgun

Butt stock ($50,000)
Flechette ammo ($50,000)
Extra ammo ($75,000)
Reload boost ($75,000)
12 gauge slugs ($75,000)
Short barrel ($100,000)
Rail mount ($100,000)
Laser sight ($150,000)
Bigger magazine ($150,000)
Red dot sight ($200,000)
Silencer type1 ($200,000)

Misc. upgrades

Pain killers ($50,000)
7x50 zoom binoculars ($50,000)
Improved lockpick ($50,000)
Kevlar vest ($75,000)
Enhanced detonator ($75,000)
Adrenaline ($100,000)
Flak vest ($100,000)
Extra mine ($100,000)
Cratt Schultz lockpick ($150,000)
Foil padded suitcase ($150,000)
Flexible flak vest ($200,000)

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

First Mission Complete (25 points): Successfully complete the "Death Of A Show Man" mission.
Rookie Mode Complete (25 points): Successfully complete the game on the Rookie difficulty setting.
Normal Mode Complete (50 points): Successfully complete the game on the Normal difficulty setting.
Expert Mode Complete (75 points): Successfully complete the game on the Expert difficulty setting.
Professional Mode Complete (150 points): Successfully complete the game on the Professional difficulty setting.
Silent Assassin (25 points): Get a Silent Assassin rating.
Normal Silent Assassins (25 points): Get five Silent Assassin ratings on the Normal difficulty setting.
Expert Silent Assassins (50 points): Get five Silent Assassin ratings on the Expert difficulty setting.
Professional Silent Assassins (100 points): Get five Silent Assassin ratings on the Professional difficulty setting.
Fully Customized Silverballers (25 points): All custom Silverballer components purchased.
Fully Customized SMG Tactical (25 points): All custom SMG Tactical components purchased.
Fully Customized SP12 Shotgun (25 points): All custom Shotgun components purchased.
Fully Customized M4 (25 points): All custom M4 components purchased.
Fully Customized W2000 Sniper (25 points): All custom W2000 components purchased.
All Firearms Collected (100 points): All firearms collected and displayed in Hideout.
Tier 2 Kruger Schmidt (5 points): Tier 2 of the Kruger Schmidt upgrade shop unlocked.
Tier 3 Kruger Schmidt (15 points): Tier 3 of the Kruger Schmidt upgrade shop unlocked.
Tier 4 Kruger Schmidt (20 points): Tier 4 of the Kruger Schmidt upgrade shop unlocked.
Accidents Do Happen... (20 points): Perform a successful accident kill.
47 Kills In A Mission (20 points): A mission has been completed with exactly 47 kills.
Notorious (20 points): 47 is the World's Most Wanted.
Redemption (50 points): At the end of the game, rapidly flick the Left Analog-stick in any direction when you are lying on your death bed. When you wake up, kill everybody so that there are no witnesses.
High Roller (50 points): Accumulate $5 million.
Special Rating (50 points): Get ten or more head shots.