If you foretell a modal double-faced card, the foretell cost will be based on the mana cost of the face you cast from exile. For example, if you foretell Kolvori, God of Kinship/The Ringhart Crest, you can cast Kolvori by paying {G}{G} or The Ringhart Crest by paying {G} on a future turn. If you foretell a modal double-faced card whose front face is a nonland face but whose back face is a land face, you can’t play that card as a land.