Bunny

The Bunny is an NPC added in the 1.0.4 patch. It can be seen on many of the Terraria logos, and spawns on grass blocks without backgrounds. It is normally a friendly creature with 5 HP, which is damaged by monsters, and is incapable of dealing damage. However, if you throw Vile Powder on it, or there is a Blood Moon, it turns into a Corrupt Bunny.