Bunny

Bunny in Slime costume for Halloween Internal NPC ID: 303

Bunny in Santa costume for Christmas Internal NPC ID: 337

A, which appears rarely in place of a normal bunny. Internal NPC ID: 443

A Bunny with a Party Hat for Internal NPC ID: 540 (insert image here)

A bunny with a gem colored sprite for underground towns

If critter hunting on desktop, the best way to spawn any gem bunny or squirrel is to make a cavern town (not underground, it is one layer deeper) with three NPCs having moved in.

Trivia

 * The Bunny is an iconic Terraria element and can be seen on many of Terraria's logos.
 * Humorously, a bunny wearing a slime costume is labeled as "slime" when moused over.
 * During Halloween, there is also a Slime wearing a Bunny costume. Bunny Slime.png
 * Bunnies are the most common Critters in Terraria, and are usually the first ones a new player will see.
 * The loading screen tip of "Killing bunnies is cruel. Period." may be a reference to The Elder Scrolls V: Skyrim, in which you can track the number of bunnies you have slaughtered via the menu.

History
Hase Lapin 토끼 Króliczek Bunny Кролик 兔兔