Each pack will contain 4 cards:
Slot one is a promo-stamped rare or mythic rare from the most recent set. Could be any rare or mythic rare.
Slot two is a promo-stamped rare or mythic rare from a short, curated list. These will be from Standard-legal sets, and they'll be hand-selected by Magic’s design studio. These lists will be public.
Slot three is a foil promo-stamped alternate art basic land.
Slot four is the promo slot. With each Standard-legal set there will be a selection of special, season-specific cards with special treatments such as alternate frames/alternate art promos.