Update (Wednesday, 1/15) – Kingdra is XY39.
It was probably going to be revealed ahead of prereleases anyway, but another social media leak has revealed that Primal Clash‘s prerelease promo is an alternate artwork version of Ancient Trait Kingdra. We’re not sure what promo number it is.
Primal Clash prereleases will take place January 24th, 25th, 31st, and February 1st. To find one near you, use Pokemon.com’s event locator. The set’s booster packs will officially be released in stores February 4th.