Which expansion added the Pet Battle system?

Mists of Pandaria added the Pet Battle system to World of Warcraft. Released in September 2012, the expansion transformed previously non-combat vanity pets into collectible creatures that could participate in turn-based battles.

Players could challenge wild pets, other players’ teams, and dedicated Pet Battle trainers. Defeating wild pets made it possible to capture them, while the Pet Journal tracked each pet’s collection status, level, abilities, and statistics. Pets could be trained up to level 25, creating a progression system separate from the player character’s level.

The system also introduced pet families, each with different strengths and weaknesses. Team building therefore involved more than collecting rare creatures: players had to consider abilities, counters, speed, and the opposing team’s family types. Daily trainer battles added repeatable rewards and helped turn the feature into a long-term side activity.

The main confusion is between vanity pets and battle pets. Vanity pets existed before Mists of Pandaria, but the expansion was responsible for giving them a formal combat system. Cataclysm preceded it, while Legion and Warlords of Draenor expanded the feature later.