Craft is an activated ability found on transforming double-faced permanents. Craft abilities require you to pay mana and exile the permanent itself along with specified materials from your battlefield and/or graveyard, then return the card transformed under its owner's control.
Brass's Tunnel-Grinder rewards filling the graveyard before transforming into a powerful land, while Matzalantli, the Great Door asks you to assemble enough permanent types for its transformation. Craft decks often treat the graveyard as a collection of raw materials rather than simply discarded cards.
