Hello!
Here’s more information that was found about Pet Battles in the 5.1 PTR patch.

Pet Battles

  • A new item has been introduced that can be used to upgrade the quality of Battle Pets: Battle-stones.
    • Battle-stones are available in two basic types, general purpose Battle-stones that can be used to upgrade the quality of any pet, and family specific Battle-stones, which can only be used to upgrade pets of a specific pet family. Pets over level 15 upgraded in this way can lose up to two levels in the process.
  • Several classic Raid bosses now have a chance to drop new Battle Pets. The new pets can be obtained from bosses in Molten Core, Blackwing Lair, Ahn’Qiraj, and Naxxramas.
  • Abilities that have been used will now continue to cool down for pets when they are not the active pet in a battle.
  • Pets previously removed from the Safari achievements have been added back to the criteria of those achievements now that they’re back in the wild.
  • Players that defeat Aki the Chosen at the culmination of the Battle Pet quest lines can now follow a new line of Battle Pet quests and associated daily quests that allows players to battle against Pandaren spirits.
  • The Dragon Kite can now be used in Pet Battles.
  • The Imperial Silkworm and Imperial Moth pets can now be created by Tailors.
  • A number of pets that could previously only be found accompanying other pets into battle can now be found roaming the world.
  • A number of new capturable pets can be found in the world from pet families that were once more sparsely populated.
  • Fixed an issue that would prevent some pets captured in Pet Battles from correctly saving their skin color once added to the Pet Journal.
  • Player versus Player Pet Battles now award more experience.
  • Large plants and bushes in the environment that interfered with visibility during Pet Battles while now fade out of view during the match.