Wraith/Doom 3

The Wraith is a monster in Doom 3 and its expansion packs. They are small hunched over humanoid creatures, shorter than an Imp, characterized by their mandible-like jaws and -like arms, giving them more of an appearance of a bat.

The Wraith first appears in the EnPro facility. It's debut intro features the Marine finding a wounded survivor of Bravo Team, who gives him a transmission card. The monster is shown to stealthily climb down a wall, right behind both marines, then hides in cover for a single second before leaping onto and killing the wounded marine before facing the player with its jaws splitting open horizontally, letting out a frightening scream.

Combat characteristics
Like the Maggot, Wraiths are only limited to melee; they will attack by using their falx-like appendages on the back their arms to slash the player up close.

Wraiths rely on their "teleportation" ability in order to ambush players. They disappear for a few seconds before suddenly reappearing right in front of the player, although their distance to teleport is generally limited to around 5 meters if players are able to move further away from the monster. Further, if the player stays a bit close to where they last teleported, Wraiths will simply wait to reappear until the player approaches so they can close in to attack.

Tactical analysis
Like Imps and Maggots, Wraiths are mid-level humanoid-type demons that are relatively easy to dispatch individually. However, inexperienced players will sometimes get confused based on when to attack during the monster's teleportation phase. The best time to attack is immediately after they start re-appearing, as they will remain vulnerable for a few seconds. Once they initiate their teleportation, they will remain invulnerable again.

The best weapons to take down an individual Wraith at close range are the Chainsaw and the Shotgun. The latter is especially useful as one point blank shot up close will instantly neutralize it. Other weapons like the Machine Gun and even the Pistol (2-4 shots) can also work well, provided if the player can take them from a safe distance.

While an individual Wraith may pose as a minor threat, they are potentially more dangerous when they come in packs or with other demons. Their ability to teleport can most likely block a safe retreat for an overwhelmed player. To avoid this, use either the Chaingun or the Plasma Gun to immediately take out a pack of them. Alternatively, since Wraiths can only teleport through a linear path, you can also hurl some Grenades which can cause them to get caught in the explosion, killing them instantly.

Trivia

 * In the Making of Doom 3 book, id wanted the Wraith to form out of a cloud of insects, to hide in bodies and such, but this concept was scrapped since the player wouldn't even be able to tell what the cloud was in the dark environment.
 * The Wraith's teleport ability may not be exactly teleportation. For one thing, it's not instantaneous. Also, while teleported, they still cannot travel through solid objects such as crates, shelves, or walls, and when they teleport through doors, the doors will open. Furthermore, their footsteps can still be heard after they disappear. This suggests that Wraiths don't actually teleport, but rather "phase" into a state of existence where they cannot be seen or attacked. If that is the case, then they would be similar to that of the Spectre. However, these might be merely distracting illusions or gameplay element.
 * Interestingly, the Wraith is the only enemy in the game that the player starts fighting before it makes its debut cutscene.