Beginning May 15, select WoW players will be invited to participate in a small-scale, focused closed beta test. Players will also get a chance to help put our servers and technology through their paces in a series of stress tests running from May through July—you can opt in now through Account Management and select the WoW Classic beta. Subsequent stress tests will extend the opportunity to even more players. Level caps will also be in place to ensure we’re emphasizing the “stress” in “stress test”
World of Warcraft Classic lets you play the game as it existed almost 15 years ago, upon the release of the 1.12 "Drums of War" update. Blizzard says it considers that era to be the correct balance of the game resembling its original launch state while also having ironed out some of the rough spots of launch. This version is also including some updates under the hood, like modern server infrastructure and Battle.net social features.
Different qualities aren't limited only to wild pets—many rare World drops and special non-wild companions have had their stats boosted. For example, the world-drop dragon whelps (Azure Whelpling, Crimson Whelpling, Dark Whelpling, and Emerald Whelpling) are of [rare] quality. Check your Pet Journal to see the color-coded rarity of your non-wild pets.
2. Achieving. There are many pet battling achievements in game, and following the natural trail through the Taming [Continent] achievements up to Pandaria, and then on to the Spirit Tamers, Beasts of Fable and the Celestial Tournament was an epic journey for me and for many others. It's well worth doing. The Celestial Tournament is still, IMO, the pinnacle of PvE pet battling. However, WoD and Legion and BfA have added more battling achievements.
Along with revealing the WoW Classic release date, Blizzard also listed plans for both a beta and stress test of the game. Players who opt-in for the testing on their account manager page and have an active subscription will be randomly selected for the beta starting May 15. Then the developer will have three stress tests where players can log in to play the game for a short period of time on the following dates: