Psycho

The Psycho is a Hardmode, post-Plantera enemy that spawns during the Solar Eclipse event. The Psycho will initially spawn in a nearly invisible, stealthed state, waiting for the player to damage him or draw near before he fully reveals himself and starts attacking. An attack made by the Psycho while in stealth will deal significantly more damage than an ordinary hit, similar to the function of the Psycho Knife it drops.

Trivia

 * The Psycho is a reference to Michael Myers from the 1978 film Halloween, though the sprite more closely resembles Jason Voorhees from the Friday The 13th series.
 * For some reason, despite following the Fighter AI, the Psycho cannot open doors, nor does it interact with them.