On Thursday, Wizards of the Coast revealed the Magic: The Gathering Mystery Booster, a set designed for Chaos Draft, which Verhey describes as "Chaos Draft meets Future Sight". The set features mostly reprints, and there are some never-before-seen playtest cards included in each booster pack, but according to MTG head designer Mark Rosewater, only one of the two editions will include them.
On his Blogatog, Rosewater responded to a fan's question about the playtest cards' availability: "The playtest cards are just part of the Convention version," Rosewater said. "The store version will have something else in that slot. There will be an article on Monday about the Mystery Boosters that will share what."
The Mystery Booster will have two available versions: the one for conventions and Grand Prix events, and the other for local game stores. WotC still hasn't revealed what will replace the playtest card slot for the store version but now we know that fans will have to attend MagicFest or conventions supported by Wizards to join a Chaos Draft with Mystery Boosters that contain playtest cards.
The playtest cards seem more like a part of an Un-set because some of them have weird new mechanics we could potentially see in the future. The mechanics in playtest cards include Aggressive, Bank, Challenge, Firstest Strike, Four-faced, instant tokens, interplanar, land tokens, Kinfall, Landship, Legacy, manabound counters, Megalegendary, Motivate, plot, booster, quadrupling, Ransom, Reflect, Requirement, Reverse miracle, sorcery tokens, Spark, Scrycast, Tasty, Underdog, and Whammy deck. These playtest cards are not playable in Constructed formats, only in Chaos Draft.