GS is the first promotional Bakugan Battle Planet card set. These cards were given out at the American Bakugan GameStop event on June 1, 2019, and then later during a Canadian Toys R Us event on September 15, 2019.
Poster for the promotional GameStop event
Poster for the Toys R Us event
These cards are Foil/Hex versions of existing Battle Brawlers cards except they are given the Bakugan Elite design where the artwork goes through the borders.
List of Cards in the first promotional Battle Planet card set