Discover

Covers the Discover keyword introduced in Lost Caverns of Ixalan, which exiles cards from the top of the library until a nonland card with mana value less than or equal to the discover number is found, then casts it for free or puts it into hand. Geological Appraiser triggers Discover 3 on entry, and Quintorius Kand offers Discover as a loyalty ability. Distinct from cascade.cost_alternative, which replaces a spell's mana cost with a different payment on the spell itself, and from cascade.free_spell, which lets you cast a card from hand by exiling other cards. Discover specifically chains a free cast off the library based on a numeric threshold.