Perfect Dark Zero

In the Desert Multiplayer map, there is an area where you can take cover and see through the wall. In order to do this, you must have Bases 2 and 4 open. Go into the cave temple base, then go through the hall, and up the sand hill, not the stairs. Go in the little courtyard from either entrance then turn left. There should be a bowl near the wall. Stand as close to the wall and as far in as you can into the wedge created. While standing, go into cover. If done correctly, you should be able to see through the wall. This is most effective during the Infection game type with the Plasma Rifle. Hide there and whenever you see a skeleton, use the secondary function (invisibility). They will usually walk out because it is very difficult to see you.

Finish the mission(s) with these following sniper rifles to bring them into other missions.

In order to unlock a weapon, you need to start a level that has that weapon in it, find that weapon, and finish the level with it. Simulations such as the level 0 are an exception; you don't get to keep the weapons, because they are not real

The following list is most unlockable weapons, the type of weapon, and the amount of carrying capacity that it takes up. In the second column is the mission that the weapon first appears in.

The viblade is in the room with all the laser tripwires, on a stand in the center
The M60 can be taken from a guard when you fail to get let in by the front gate guard

Oh, and sniper take up 3 inventory spaces, making them unwieldy, but the jackal and shockwave can be found in rooftops escape, and bridge assault respectively.

The following is a list by level of all the weapons and where to find them. Note: The first and last level do not count for getting weapons. To get a weapon to keep for later use, keep it in your inventory at the end of the level. This is also useful with the "Easy Weapons" trick. These weapons were all acquired on Agent mode.

Datacore: Demolition

P9P (Pistol): You start with this gun.

Nightclub: Stakeout

DEF-12 Shotgun (Close Combat): Find on the enforcer in the beginning (after you scan him).

Falcon (Pistol): Found on almost any guards, such as the first two.

Frag Grenade (Thrown): Hidden behind a vent in the basement. The stairs leading down are located in the back right corner of the nightclub from the front door. After you have gone down the stairs there should be two vent coverings. Break them and get the grenade.

UGL Liberator (SMG): Found on the guard on the third floor. He should have two of them.

Subway: Retrieval

CMP-150 (SMG): Found on some guards.

DW-P5 (SMG): Found in the only open storage crate after you have gone through the parking garage.

Rooftops: Escape

Jackal (Heavy): Found on the sniper if you did not shoot it off the building. The easiest way is to put away any weapon you have (Up) and use disarm (RB).

M60 (Heavy): Found once you get to the fire doors. Go past the fire doors and lock pick the door. It should be standing atop an artillery box next to the guard.

Mansion: Infiltration

Magsec 4 (Pistol): Found on all guards at the beginning of the level.

Viblade (Close Combat): Found once you get in the mansion. It is standing on a pedestal in the middle of the laser maze.

Laboratory: Rescue

KSI-74 (Assault): Found on almost all blue guards.

Magnum (Pistol): Found on the yellow suited guards that come once the alarm is triggered.

River: Extraction

Rocket Launcher (Heavy): It is recommended to get this weapon when in Co-Op mode, as it is quite difficult to get. Once you get outside, open the gate and kill the guards. On the hovercraft that you take, press Y when by the gunner to switch for another heavy weapon (M60 and Plasma Rifle only).

Trinity: Infiltration

Combat Shield (Close Combat): Found on one of the guards after you picked up Dr. Carrol. There are two guards once you find the round walkway the leads to the lower level.

Hawk Boomerang (Thrown): Found in one of the boxes in the beginning of the level. This is easier to get after you have picked up the X-Ray goggles in the weapon cases to the left once you start.

Trinity: Escape

Psychosis Gun (Pistol): Found on most scientists throughout the level.

Jungle: Storm

RCP-90 (SMG): You can find this either on the assaulting guards or atop of boxes by the left wall. Try using this on that level every time you play. Secondary (RB) makes an outline of red around your enemy, with the lost of some accuracy.

Temple: Surveillance

Frag Grenade (Thrown): Found on some of the guards. This may be difficult to find.

Laptop Gun (Assault): Found on one of the two guards after you have gone down two levels. If one of the guards plants one, reprogram and pickup. It should say reprogram once you get close to it.

Multimine (Thrown): Found on the guard that is either on the water bridge, or around the corner after it.

Plasma Rifle (Heavy): Found at very end of level on any of the Phantoms.

Outpost: Rescue

FAC-16 (Assault): Found in one of the weapon cases after you rescue Jonathan.

Flash Bang (Thrown): Found on one of the guards in the room before you go through the double keypadded door.

Bridge: Assault

Shockwave (Heavy): Found on the fallen Carrington sniper once you go to aide Jonathan's team.

Super Dragon (Assault): You may have found this gun before. Found on some of the guards on the bridge.

At the beginning of Mission 7, before or after you kill the two brothers, there are four lockers on the right wall of the side of the bridge that you start at. If you are looking directly across the bridge and turn 90 degrees, you will see four lockers on the wall. In one of them is a pair of X-ray goggles. If you look around in the wooden crates on the side that you started on, there should be a new weapon called the Hawk. It is a disk that you can throw and slice people with.

Get to the second level of the stage. Once you enter the corridor that has the two traps, instead of continuing past the traps, turn around and enter the door behind you. Inside there should be two guards. On a crate near one of the guards will be the X-ray goggles.