Since this is Japan’s annual “High Class Pack” set, its main attraction will be its enormous amount of alternate art secret rares. For example, last year’s Shiny Treasure ex featured 190 cards in its main set and a whopping 170 secret rares. None have been revealed so far.
Each Terastal Festival ex booster pack will contain 10 cards instead of the usual five, including a guaranteed Pokemon ex. The larger packs, guaranteed hits, and secret rares are what define a “High Class Pack” set.