Wraith

Wraiths are Hardmode ghost-like enemies who can travel through blocks and 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

 * Wraiths can be attacked through walls with melee weapons or any other weapon whose attack animation does not end when it hits a wall. This makes spears especially effective.
 * Any structure built at least six tiles above the surface will prevent a Wraith from levitating up and into it.
 * Breaking altars is an efficient method to get Wraith Banners and the Fast Clock without using the Wraith Statue.
 * If the player is in or slightly above the Ocean, a Wraith can spawn below and to the sides of the player. The Wraith can then float towards and attack the player.

Trivia

 * According to the Collector's Edition trading card, those who are devoured by an Eater of Souls become a Wraith. This might not be the only way of creating Wraiths, since they are not exclusive to worlds with a Corruption biome, and will still spawn in Crimson or purified worlds.
 * The card also has a typo where "devoured" is spelled "devourered.