In addition to the many mobs and animals present in Terraria, you can also take a pet of your choosing along with you on your journeys. Some of these pets can only be obtained through boss rewards, but some can simply be found through fishing or spelunking. Regardless, these pets provide no practical benefit and will simply follow you as closely as possible.
These pets are immune and provide you with no ambient or combat effects. However, it can help you complete a theme for a character’s design or simply give you something to smile about as you travel throughout the world. There are 2 types of pets, light pets and standard pets. Light pets can light your way if it's dark, some of them emit dim light and others emit bright light. The standard pets can be used as a good companion or something to smile about.