Frankenstein

Frankenstein is a Hardmode enemy that spawns only during a Solar Eclipse, during which they are as common as a Zombie. They move much faster than a Zombie.

They are one of only two enemies that drop the Broken Hero Sword, which is necessary for crafting the most powerful sword in the PC game.

Trivia

 * Terraria continues a common mistake about Frankenstein. Frankenstein is the name of the doctor who created the monster, not the monster, himself.  The monster is typically called "Frankenstein's Monster", or a "Frankensteinian Monster" for a more generic term.