Wraith/Doom 3

The Wraith is a monster in Doom 3 and its expansion packs. Wraiths are limited to melee attacks with their -like arms, and run forward to attack the player. They possess what appears to be a "teleportation" ability, disappearing for a few seconds before reappearing several feet ahead of their previous position. It can be easily mistaken for an Imp while it's being summoned. Unlike an Imp, Wraiths are hunched over and present a lower, wider target profile. Furthermore, Wraiths have only two eyes and a set of mandible-like jaws, and look more like a bat than a human.

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 Imps and Maggots, Wraiths are mid-level humanoid-type demons that are relatively easy to dispatch individually, but who can attack in groups of up to several in the same area. When paired with other hellspawn, the danger they present increases, as they are fast enough to block the player in, and attack while they are distracted with other threats.

When they "teleport," a pentagram appears on the ground where they are standing and fiery orange streaks shoot up as they disappear. Once the Wraith fully disappears, so does the pentagram on the ground. At this point, the Wraith is invisible, but is still bounded by physical objects, such as doors, shelves, crates, etc. as it moves about, and its footsteps can even be heard. A few seconds after disappearing, another pentagram appears on the ground where the Wraith is currently standing and the fiery orange streaks then move down the Wraith's body as it reappears in the center of the pentagram. Once the Wraith fully reappears, the pentagram again disappears, and the Wraith is then free to move and attack the player.

Wraiths prefer ambush tactics, even after being seen. They try to teleport themselves to places where the player is not looking to ambush them. Though their attacks do little damage, they should not be underestimated, as they move and attack quite fast. They can easily pin and seriously damage a distracted player.

Tactical analysis
Wraiths cannot be killed while teleported, however it takes them about a second to disappear or reappear, during which they cannot attack or move. This makes them extremely vulnerable to being damaged or killed. They can easily appear to attack the player's flanks, and their rapid and erratic movement makes them difficult targets.

It's a good idea to throw a grenade their way. Another good tactic is to wait for them to get close and eliminate them with the chainsaw or the shotgun. In addition, they can be easily eliminated with the machine gun or plasma gun at medium range.

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.