Dogs and Cats (aka "pets" or "critters") are mobs that can be tamed to follow and fight for their owner. Dogs and Cats can be found in the Underworld randomly throughout all levels or in Deep Cave, and have a chance of spawning from an Altar. To tame a pet after you found one simply drop raw or cooked meat or fish 1 at a time onto the floor around the pet and wait until it walks over to the meat. It will "eat" the meat and say "arf!" or "meow" which means that you are now a proud owner of a pet!
Pets can also be given Costumes to look like some creatures in the game.
Controlling your pet:
To command your faithful pet, two simple commands can be issued. They must be done using area ("local") chat by either saying "stay" or "come". The words must be written exactly that way. For the commands to work, the pet must be in the same "screen" as the player.
The command "stay" will make the pet stand where it was told to and stop following their owner, though they will pace around a small area and can wander off if their loyalty gets too low. Pets won't join fights or defend you from mobs if they are told to stay. They will still defend themselves if attacked directly.
The command "come" will make the pet follow you if it was told to stay and will make the pet teleport to where you are standing. If a pet is in your way, re-issuing the "come" command will generally move him. Pets that are following you will target a monster if monster hits you or is attacking the pet.
If multiple pets are present they will all obey the same order together. Several pets can follow a player at once. If you have multiple pets and are trying to separate them try going through multiple doors or going to the very fringes of the local chat area to call just one. This may take several attempts.
Pets can be healed using bandages and each food item they eat (including dishes from pots) restores 10 points of their health.
Training your pet:
Beware! You can harm your own pet with pvp enabled, always hold a non-weapon (i.e. shovel, bandage, repair kit, shears etc. ) while selecting them.
Pets can be trained so their stats increase. This is done by letting your pet kill other mobs (any type of monster works). Each kill they make grants them 10 max health points more and increased damage as their health increases. At higher health levels it takes more than 1 kill to gain that 10 health. The pet only needs to land the killing blow so you can help them when they are still weak.
The maximum health for a dog is 2000, at which they deal ~80 damage per hit on average. Max armor on a dog is 10. The maximum health for a cat is 1200, at which they deal ~90 damage per hit on average. Max armor on a cat is 5. Costumed pets will have the same attributes as the pet they were before being altered.
A good place to train pets is to kill the animals around Galebrook or Wellington. At around 250-300 health it is recommended to fight snakes which are found in larger numbers at Snake Pit and South Sands Desert.
Always bring a bandage to heal your pet, and/or a stack of food. Keep an eye out for hostile players who may want to kill your pet.
Housing your pet:
It is recommend that you keep your pet indoors in a room separated from any room that stores food. Pets will eat herbs, honey, and cooked or uncooked food provided it is not "old" (though pets will eat old mystery meat with no costume effect). They do not eat aloe. Placing a non-food item on top of the pile of food should deter them from eating it if space is limited. If your pet eats food that belongs to another player it may become loyal to that person instead of you.
Placing a pet in a hallway or small space that is used by other players may cause aggravation to the other players and lead to your pet dying under mysterious circumstances. Pets that you own may also be tamed by other players who have access to them after a few days of diminished loyalty.
When you keep your pet at home periodically check its health even indoors. As the pet's health drops and time passes it will lose loyalty to you and eventually start roaming as an untamed ("feral") pet. Telling the pet to stay near a bed will help it keep it's health up, however to maintain both health and loyalty you should periodically drop some food for it to eat. Pets will become "feral" after about 7-8 days of not being fed by the owner.
If you keep your pet outside keep in mind that aggressive mobs such as wolves or snakes (or rarely, Chaos) can spawn on grass and attack your pet. If your pet has max hit points it should be able to defend itself from most mobs, but a Chaos may eventually kill it.