Pets are NPCs that follow and usually assist the player in some way. In addition to Starter Pets the player can tame many types of animals and monsters. The home planet pets are more aimed towards companionship while the space monster pets are more suited for combat.
A monster can be caught by throwing a Capture Pod at it, which is crafted at the Pet Station. The monster can be a critter, passive, aggressive, or even a large monster, but it has to be under 50% health to be caught. Pets such as critters and dogs cannot do anything. Other pets will no longer attack NPCs and villagers, and will only attack hostile monsters or NPCs. Passive monsters must be attacked by the player for the pet to target them. They will teleport back to you though if you are more than 36 blocks away. Pets will also follow you to your space ship if you beam up, and to other planets.
If a pet that is following you is killed, it will return to its capture pod. Capture pods with dead pets in them have no red light, and attempting to use them will make a shaking sound. Dead pets must be placed at a Pet Healing Station to be revived before they can be used again.
From version Offended Koala, pets leveled up when they killed around 21 monsters. They gained health and damage boosts from leveling up. They gained experience by dealing the killing blow to any kinds of monsters.
As of version Cheerful Giraffe, pets no longer level up. No matter what tier planet a pet was caught at, their attack, defense, and health depend on the player's armor. Armor with more defense boosts will give your pet a higher defense, and armor with more attack boosts will give your pet higher attack.
- It seems that pets can teleport with you everywhere, although, there might be some instances where they are not able to.