Wraith

A Wraith is a mob that can be found during Spooky Festivals during night. It has 15 health, and every attack deals one heart of damage. The Ghoul Buster deals two hearts of damage instead.

Trivia

 * The Thunderlord and Thunderbolt were previously bugged, and dealt true damage to the mob ignoring their defense. This was patched in a later update.
 * The wraith may be a reference to the Wraith in Terraria with similar sounds and texture.