Wraith

A Wraith is a mob that can be found during Spooky Festivals during night. It has 15 hearts, and every attack, no matter how good the sword, only deals one heart of damage. Thunderlord and Thunderbolt was bugged, and dealt true damage to the mob ignoring their defense. This was patched in later update. The wraith is a reference to the Wraith in Terraria with similar sounds and texture.