Stealth
The best weapon in your arsenal is stealth. Your ability to slip into a room and remain undetected until you attack and then quickly melt back into the shadows is what makes you such a terror to your enemies. They never know where you are and where you will hit next. And if you are truly a master of the shadows, they will never even know you are there until that first bullet hits them in the neck.
When you are invisible to the enemy, your view turns black-and-white. You can remain in cover like this as long as necessary. Use it to survey each scene and deduce the best path through your resistance, whether that is dropping into full view and opening fire or staying in the shadows as long as possible, eliminating your enemies with kills that do not reveal your position.
You must master several stealth tactics to survive. And you must learn to use them in tandem, as you can actually drop every target without being spotted if you are methodical with your stealth techniques. Use the hint of a Last Known Position to lure an enemy into your firing line, or scurry up a drain pipe to dish out the lethal Death from Above move.
Lights Out
There are many ways to remain undetected, such as hiding behind a wall or crate. But no cover is more useful than the dark. Seek out the shadows whenever possible, such as the dark corners of a ballroom or on top of an office. You can also make your own shadows, if necessary.
Most lights can be shot out. If the target cursor appears red over a light, pull the trigger to blast it. Shooting out lights can draw attention, though, so be mindful of enemies in the area. They may wonder why a light suddenly went out behind them or be drawn in by the sound of breaking glass.
Shoot out lights to obscure your trail, such as popping headlights to cover an enemy body in shadows.
Pipes and Ledges
One of the best places you can hide from detection is on pipes that crisscross ceilings along hallways and over rooms. Most pipes are accessed by pulling yourself up a vertical length of pipes, usually running up a wall. However, some are low enough that you can jump straight up and grab them. Once on a horizontal pipe, you pull yourself up and swing your legs over it.
While shimmying along the pipes, you remain completely out of view - as long as you don't attract attention. If you open fire with a machine gun from a ceiling pipe, every pair of eyes in the room will look up. Hanging from a pipe with eight guns pointed at you is a terrible, terrible place to be.
However, pipes are excellent vantage points for not only gathering intel on a situation (monitoring enemy patrol routes, spotting environmental hazards), but also killing your enemies. Arming a silenced weapon and pulling a mark-and-execute from a pipe is a great opening move when facing a room full of enemies.
Using a silenced weapon and shooting an enemy by himself while nobody is looking is another good kill that avoids detection.
While hanging from a pipe or ledge, you can use gear, such as throwing a grenade or planting a mine.
Pipes are preferable because your aim is so expansive - you have a 360-degree view of a room. However, ledges are also useful for moving above the average mercenary's line of sight. If you see a ledge along a wall or you are next to a ledge (such as on a balcony), jump up and grab it. You can then shimmy left and right. If you are hanging from a ledge on a wall, you can only aim to each side and behind you.
While hanging from a ledge like a balcony, you can poke your head up and target an enemy. But like peeking out of cover, this exposes you. You might get spotted. But maybe that's your goal. Read the Last Known Position section to see how this is incredibly useful at times.
Death from Above
While hanging from either a ledge or a pipe, you can perform the Death from Above kill. As an enemy moves beneath you, a button prompt appears onscreen. Initiate the move and you jump down, crashing into them.
The takedown is relatively quiet because you muffle their surprised cry as you smash their head into the floor. However, if you do so in an illuminated room or within close earshot of another enemy, you are easily spotted.
Smash into an enemy in the shadows and then scurry back to the pipe to avoid detection and prep another kill.
Windows
Windows are a devilishly clever tool for dispatching enemies as well as gathering intelligence. Most buildings have windows you can hop through and then hang on the ledge outside. If you have a wall of windows before you, though, you have a virtual shooting gallery.
The first thing to be mindful of with windows, though, is whether they are open or shut. To be silent, make sure you slide open a window before attempting to pass through it. If you jump through a closed window, the shattering glass makes enough racket to draw a lot of attention from nearby enemies.
Now, that has its uses. The noise from a shattered window will pull enemies to one particular window. You can then scurry to the left or right on the ledge outside and flank the enemies investigating the broken window.
An enemy checking a broken window or a window with your LKP often sticks his head out to look around. He will shoot you if he spots you. But for one moment, all that is exposed is his head. Draw a bead and take him out.
You can also use a bay of windows to flank enemies. Jump out a window and then slide along a corner ledge to peer back in the room and target your enemy's back.
Perhaps the most fun you can have with a window, though, is ambushing an unsuspecting enemy standing next to it. Slip up to an enemy with his back to the window. Then, follow the onscreen prompt to reach in and seize him. You yank him right through the window and throw him to his death. If the window is open and nobody is looking, this is a silent kill.
You may need to open the window in some cases. Opening a window can draw attention, so be sure other enemies in a room are looking elsewhere before you lift the glass.
Last Known Position
Last Known Position is one of the best tricks you have to outsmart your enemies. Using LKP, you can lead enemies around rooms like lemmings, as they desperately try to be the one who takes you down. But the catch is, they are only chasing your ghost. By the time they reach the LKP, you're gone. And that's when they know they're in real trouble.
LKP is represented as a white outline of yourself when you were spotted. If you were leaning out of a door or shimmying along a pipe, your outline is then fixed in that action. Enemies will communicate the LKP to each other and they will focus their attacks on it. Maybe they will shoot at your LKP or attempt to flank it. It doesn't matter. What matters is that you put some distance between you and the LKP and then use it to your advantage.
Sometimes, your LKP is a total accident. An enemy got a peek at your position or you were a half-second too slow jumping out a window. But even if you did not plan your LKP by purposefully leaning into view, you can still make the most of it.
The easiest use of the LKP is disappearing. If multiple enemies are converging on you and you spy an escape route, poke your head out of cover to create a LKP and then dart through the shadows.
As your enemies focus on your LKP, plan your attack. If multiple targets gather around an LKP, mark them for execution. Circle behind a solo enemy investigating a LKP and hit him with a close kill.
Set traps by getting spotted at a door. As the enemy approaches your LKP, lunge and grab them for a close kill.
If spotted on a pipe, use a countermeasure like a flashbang to divert your enemy's eyes and then move away. When they look back up at your LKP, you are somewhere else - and ready to kill them.
LKP at a window is awesome...awesomely lethal. When the enemy leans out to look for you, reach up and pull them to their death.
Interrogation
When you close in on an enemy who you need to extract information from, you can interrogate them. You can't shoot an interrogation target, but be careful not to kill them with any explosives; you need the information they have. When you get close enough to strike, grab them like you would to initiate a hand-to-hand kill. Instead of snapping their neck, you hold their throat and draw them close so they know you mean business.
Not every interrogation target is loose lipped. Some people need to be prompted to open up. When a subject does not answer your question, you need to convince them to do so by either hitting them or driving their face into a nearby object, such as a toilet, television, or piano.
Just drag them so their back faces the object and then press the interrogation button. Each object results in a different attack so no two interrogations are the same.