Skeleton Commando

The Skeleton Commando is a Hardmode enemy that spawns in the Dungeon after Plantera is defeated. It fires Rockets that explode when impacting blocks. They are immune to the Poisoned and Venom debuffs. Like the Blue Armored Bones, they only spawn in dungeon areas with a Brick Wall.

Trivia
It may be a reference to the movie Terminator as it looks like the T-101.