This gift is distributed to players via a serial code, given in participating stores to celebrate the release of the TCG 25th Anniversary Collection, starting from Oct 10, 2021. Using the Dynamax Crystal would allow Gigantamax Eevee to appear at the Watchtower Lair's Den as a max raid.
As of LGPE, wonder cards are no longer stored in saves. As such, players will not be able to inject this event into their save using PKHeX.
Format Ver.2.1.2-7, Post Updated Date:20211011_1927