The Buy-a-Box promo for the upcoming Magic: The Gathering set Theros Beyond Death includes two cards —one foil "Athreos, Shroud-Veiled", and one foil full-art "Nyx" Land, both packed inside an opaque sleeve. Customers can get one Buy-a-Box pack for each box of Draft Boosters or Collector Boosters they purchase.
However, Wizards of the Coast has announced that there's a production error in the lands in these packs: they were printed in non-foil, but a reprint with proper foil treatment is coming, and they will ship the replacement lands as soon as possible. The foil lands wills arrive in a separate shipment, after and around prerelease.
If you're in North America and Japan, expect most stores to have the foil Nyx lands available sometime around the Theros Beyond Death Prerelease weekend, January 17–19. Other regions will have to wait for the lands to arrive after that date. WotC will send the same number of replacement foil Nyx lands as Buy-a-Box packs.
Theros Beyond Death, the 83rd Magic: The Gathering expansion, is set to release on January 24, 2020. Prerelease events will take place on January 17-19.
Related: MTG Designer Responds To Whether or Not Ikoria Commander Decks Will Get A Prerelease Weekend