Shibitos are your enemies in this game. They take many shapes and forms, from humanoid to insectoid.
A shibito will become "suspicious" when he hears certain things. These are: hearing the player-character's footsteps, hearing a shout, hearing player-character's gun. During this state he'll search lazily around the nearby area, especially towards the direction where the sound was heard. This state lasts only a short time, perhaps 10-15 seconds, after which shibito will return to his usual doings.
A shibito will become "alerted" when he sees targets, such as the player-character or his sidekick. In this state he'll start searching and following you actively, putting you in grave danger. This state lasts indefinitely, ending only when he loses you from his sight or dies. After that he spends a moment in the "suspicious"-state, using the last sighting of the target as a meaningful cue.
When a shibito gets alerted, the screen will flash red (or whatever you wanted it to flash, as it's selectable from the options) and he makes a distinct sound by which you can tell he's alerted. When a shibito gets suspicious, the screen will not flash red, but he still emits a distinct sound.
A shibito doesn't die, but rather just gets "knocked out." After a short while he'll be back up. The required time differs with each shibito. After a shibito has been revived, he's suspicious for a moment before returning to the normal route.
The shibitos will never voluntarily aim each other, and they won't get damaged from eachother's hits either - with the only exception being projectiles.
Some shibitos enter the level only after you've reached some location, picked up some item, etc. Before they're around you can't sightjack them or do anything else with them for that matter. The same goes for shibitos who've disappeared: they're outside your sphere of influence in every possible way. If you had a sightjacking slot reserved for a disappearing shibito, it'll disappear as the shibito disappears – if you want it back you have to manually set it again when the shibito is available again.
During both normal gameplay and sightjacking, you can hear various noises from your enemies. Most of these are obvious, like the sounds they make when they get alerted, etc. But all of them have something which could also be called "taunts," special noises which they make for no reason at all, at random intervals. They are often very high in volume and sudden, though not always. If these "taunts" come from your ex-player-character, they often contain some clear speech clips which reveal their true intentions! These taunts may be (at least partially) different during the gameplay than when sightjacking. Some special voices are only heard when they are alerted or become alerted.
During sightjack, you also hear all the shibitos breathe loudly. They have a different breathing voice if they're alerted, and it turns back to normal when the alert fades out - usually. Sometimes their sounds remain alerted beyond their actual physical state, and you have to re-sightjack them in order to hear them breathe nice and slow again.
These are shibitos that fly. They sport a pair of insect wings and move around the area carrying a revolver or a rifle. Most of the rules that apply to other projectile weaponry using shibitos apply to them too, but they have a couple of unique things of their own too.
First of all, even though they can fly, they only scarcely pass over to areas that normally walking shibitos wouldn't or couldn't go. It may be a result of walls that extend high up to the air invisibly, or it may be a result of some in-game script that doesn't want them to helplessly fall inside obstacles or walls when they die. Needless to say, it does happen anyway, so the end result is that they move funnily when near walls, and they still can die inside the obstacles and get stuck in the air. The latter doesn't happen too often at all, though.
Whenever they land somewhere they immediately become de-alerted. So during this time, if you manage to surprise attack them, they die from only one shot.
They are like normal shibitos, except that they wield a revolver (that holds 5 bullets) and their routes are usually different from normal shibitos. Because of their threat's projectile nature, most if not all of the sniper shibitos' rules apply to them too.
After shooting their reserved 5 bullets, they'll reload a variable amount of bullets back in. If no one's disturbing them, they'll load the gun full again. But if the character is still near, (and the shibito alerted) they'll load only 1 or 2 bullets - this can make a difference life-or-death situations.
Also keep in mind that your character's hit box is genuinely smaller when he's sideways. This means that if you're in danger, try to be sideways to the shibito that's aiming at you. Another safety tip in worst case scenario is to start tapping the crouch-button as quickly as you can. Some of the bullets shot at you will fly over the character!
They are a certain type of shibito whose death means that all (or some) of the lesser shibitos on that level get knocked out with them.
Shibito brains elicit a different kind of behaviour than that of normal shibitos. Some shibito brains try to escape from you instead of attacking you. Some behave like other shibitos, attacking you, only being somehow more tough, acting almost like that particular level's "boss" character. Some have behaviour that takes the best out of both worlds: sometimes attacking you and sometimes escaping.
It seems that the brains, at least the escaping ones, have a curious mechanism implemented in their behaviour: they somehow know if the player-character is approaching without actually seeing or hearing him. When they escape, they also do not get alerted. This is why some glitchy behaviour occurs with some brains: they start running somewhere because of the curious implementation, then they "normally" get alerted. They don't know what to do anymore, turning irrationally when you chase them or stopping dead in their tracks and almost ignoring the player-character.
They are like normal shibitos, except that they wield a rifle (that holds 5 bullets), they never holler or strangle and their routes are drastically different from the rest of the shibitos.
The snipers have a nearly infallible aim, much better than your character's. They can see and kill you easily from distances where you'll not be able to see them. If the player-character has a flashlight on he'll be noticed from even farther away than normal.
The sniper's shot has only one exact route of reaching the target at every possible moment, unless the target is far away - that's when there's some random variation that disturbs the bullet's route and overall accuracy.
After shooting their reserved 5 bullets, they'll reload a variable amount of bullets back in. If no one's disturbing them, they'll load the gun full again. But if the character is still near, (and the shibito alerted) they'll load only 1 or 2 bullets - this can make a difference in life-or-death situations.
When a sniper sees a new target while the previous one is still visible, he'll stop shooting for a moment, becoming re-alerted. After that, he'll start aiming at the new target and eventually shoot - unless there's the previous target still available, in which case he starts shooting towards it.