Bone Lee

Bone Lee is an enemy found in the Hardmode Dungeon after Plantera has been killed. It is incredibly fast and deals large amounts of damage. They are immune to the Poisoned and Venom debuffs. They also have great knockback resistance, which makes it a formidable opponent to fight.

Bone Lee and other dungeon hardmode enemies only spawn once the underground jungle boss Plantera has been defeated.

Tips
One effective way to fighting Bone Lee is to have a fast attacking melee weapon with good knockback. This is a great spot to make use of the the Mechanical Glove and the Golem Fist. Having knockback immunity (by grappling onto the floor or using some form of a Cobalt Shield ) also seems to be a great help. Should be treated somewhat like a boss, with its fast moves, high attack damage, high defense, and one thousand health.

If you want to take a magic approach to beating Bone Lee, your best option is a Magnet Sphere. The rapid attacks from the sphere will all but immobilize him. Combined with good mage armor, you can kill him with one cast.

Trivia

 * Bone Lee's name, appearance, and attacks are all based on real-life martial artist and actor Bruce Lee.