Blizzard has introduced in Mists of Pandaria, a mini-game that involves companion pets. The old pets that you have gathered since the end of Cataclysm and also new ones, many.
In a few words, “pet battles” is a turn based game, similar to Japanese video games. The player can control one pet and fight against other pet controlled by another player or just against a pet AI.
Your pet that is finishing the fight will get XP and level up, becoming more powerful, gains damage and hitpoints and also new abilities that are unlocked at level 10, 15, 20. Level 20 seems to be the cap. At around level 10-11, you will start to get level slower, one level requiring around 4-5 won fights against players or AI.
How to start?
To start, get the quest that enables this mini-game from the NPCs from Stormwind or Orgrimmar. Click on any critter that you find around. This will start a fight.
If your pet dies after a fight, there is a button on the top-right corner of the “pet battles” interface from where you can resurrect or heal him.
To queue for a random fight with another player, there is a button on the bottom-right side of the interface called “find battle”.
During a fight against an AI pet, you can capture it, there is a button for this that will get enabled after that pet is below 25% of his hitpoints.
You can travel from zone to zone and level up your pets, each zone has pets with higher level, just as you were leveling a character, for example the pets from Duskwood are having a higher level than the ones from Westfall.
Some pets are efficient against others, for example mechanical pets will perform great against dragonkins. You should check these bonuses and disadvantages that each kind of pet has.