Emrakul, the Promised End [Eldritch Moon] XY127 you may cast the copy

you may cast the copy without paying its mana cost

Instant — Omen

Set: Dynasty Finish: Rainbow Foil Type: Action Subtype: Attack Rarity: Rare Class: Assassin Cost: 1 Power: 5 Contract - You are contracted to banish opponents' cards with cost 2 or greater

If you search your library this way

Emrakul, the Promised End [Eldritch Moon] XY127 you may cast the copySet: Eldritch Moon Type: Legendary Creature Eldrazi Rarity: Mythic Cost: {13} This spell costs {1} less to cast for each card type among cards in your graveyard. When you cast this spell, you gain control of target opponent during that player's next turn. After that turn, that player takes an extra turn. Flying, trample, protection from instants An enigma as vexing as life itself.