Bone Lee

Bone Lee appears in the Dungeon only after Plantera is dead, and it is rare even then. It ignores the wall type restrictions that decide which Dungeon enemy spawns where, so any part of the Dungeon can produce one. A Lifeform Analyzer will call it out, worth carrying so you are not caught mid jump when one arrives.

Speed is the entire problem. It crosses a room before you finish turning, it barely reacts to knockback, and two connected hits take most of a health bar in the harder modes. Reacting from the floor rarely works.

Get off the ground. Hooking to a ceiling puts you where it cannot follow, and anything ranged handles it from there. If you would rather stand and fight, a high fire rate gun like the Megashark locks it in a hitstun loop and it dies without landing a blow.

Two of the three parts for Master Ninja Gear come off this enemy and nowhere else, so it is not optional. Given the rarity, the practical route is a post Plantera Dungeon sweep with spawn boosters up. The look, the style and the name all point at Bruce Lee.