Wraith/Doom 3

The Wraith is a monster in Doom 3 and its expansion pack. Wraiths are limited to melee attacks with their falx-like arms, and run forward to attack the player. They possess the ability to teleport, 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 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, in a gruesome cutscene where the hero finds another marine, who is mortally wounded and gives the hero a transmission card. The monster is shown to stealthly climb down a wall, right behind both marines, then hides in cover for a single second before leaping onto and killing the agonizing marine and facing the player with its jaws splitting open horizontally, letting out a frightening scream.

Tactics
Like Imps and Maggots, Wraiths are mid-level humanoid-type demons who are individually relatively easy to dispatch, but who can attack in groups of up to several in the same area.

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

It is 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 machinegun or plasma gun from medium range.

They are extremely vulnerable to being chainsawed during their second-long appearing or disappearing animation.

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 isn't exactly teleportation. For one thing, it is not instantaneous. Also, while teleported they still cannot travel through solid objects such as crates, shelfs, or walls, and when they teleport through doors, the doors will open up. 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.