Lihzahrd

Lihzahrds are enemies found only inside the Jungle Temple. They initially move as ordinary walking Fighter AI enemies. As soon as their health is reduced to below 55% ( / / ), they enter their second, crawling form, which consists of a more lizard-like creature running on four legs. In this form they are much faster, have additional damage and defense, and are immune to knockback, but have reduced jump height.

Trivia

 * The Witch Doctor is a Lihzahrd, as can be seen by his green skin and tail. This is especially evident by his party quote, "I wanted to see how your kind celebrate", which would indicate he is not human. This has also been directly confirmed by Leinfors on the Terraria forums.
 * This would make him the only non-hostile Lihzahrd in Terraria.
 * The Lihzahrd shares a very similar appearance to BBC Doctor Who’s Silurian characters.