Pokemon.com has revealed the promo materials you will receive when you attend an HS-Undaunted prerelease. The promo card you will receive will be Leafeon, which originated in Japan’s Expert Deck: Leafeon vs. Metagross.
This promo card will be holo in real life, the rarity of the one in the actual set is unknown at this time (most likely will be a non-holo rare, since the two prerelease promos before were rares in their respective sets)
The sleeve design for the set was also revealed. The sleeves this time will be purple and will have yellow/gold silhouettes of Espeon and Umbreon. You will get a pack of 60 when you sign up for the prerelease.
You can check out the prerelease page here, however, no dates or locations have been posted yet. They should be up before the end of the month.
July 17th edit: Locations and dates for North America are up! As expected, there will be prereleases on the weekends of August 7th, 14th, and 21st. The reason there are prerelease tournaments after the release date of August 18th is because Worlds is taking place the weekend of the 14th.
Players outside of North America will have to wait a little while longer to get the dates and locations of their prereleases.