Swamp Thing

Swamp Thing is a Hardmode enemy that spawns only during a Solar Eclipse, during which they are as common as a Zombie. They are immune to the Poisoned and Venom debuffs. It moves extremely fast, so it is recommended to use rapid-fire weapons or weapons with high knockback. It is one of the two enemies that can drop the Broken Hero Sword, a key part in crafting the highest-end swords.

Trivia

 * Swamp Things are a reference to the namesake 1982 classic horror film.