Lihzahrd

Lihzahrds are post-Plantera enemies found only inside the Lihzahrd Temple. They initially move as ordinary walking Fighter AI enemies. When damaged below 55%, they enter their second form, which is a lizard-like creature that runs on four legs. In this form they are much faster, have additional damage, defense, and jump height, and are immune to knockback. Lihzahrds are always immune to the Poisoned and Venom debuffs.

Trivia

 * May be a reference to the Silurians, an ancient species of sentient reptiles from the BBC series Doctor Who. This is likely as there are other Doctor Who references in the game.
 * Judging from his tail and green skin, the Witch Doctor could be a Lihzahrd.