Wraith

Wraiths are Hardmode ghost-like enemies who can travel through blocks. They can inflict the Slow debuff on the player. They have black bodies, which render them almost completely invisible in dark areas, but have two glowing red eyes which are visible from within the darkness. They spawn at the surface layer at night.

Although Wraiths appear to fly freely, they can only hover slightly above the ground. They need foreground blocks to "swim" through in order to fly any higher.

Tips

 * Any structure built at least 6 tiles above the surface will prevent a Wraith from levitating up and into it.
 * Wraiths can be spawned pre-Hardmode by using a Wraith Statue.

Trivia

 * Wraiths are most likely a reference to the fantasy novels series ' by American writer, the first series in '. There, wraiths are described as black man-shaped clouds with burning red eyes, which is further referenced by the fact that they rely upon their target being too scared to move, similar to how they can inflict the Slow debuff, hindering player escape.
 * According to the Collector's Edition trading card, those who are devoured by an Eater of Souls become a Wraith.

History
Spectre 幻灵