Cheapest priced copy (Theros Beyond Death Promos): $0.49 at Card Kingdom, near mint, their price list as of .
Allure of the Unknown 
Sorcery · Rare · Theros Beyond Death · #332
Reveal the top six cards of your library. An opponent exiles a nonland card from among them, then you put the rest into your hand. That opponent may cast the exiled card without paying its mana cost.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Theros Beyond Death Promos | 207p | Rare | $0.49 | $1.49 |
| Theros Beyond Death Promos | 207s | Rare | — | $0.79 |
| Theros Beyond Death | 207 | Rare | $0.49 | $0.49 |
| Theros Beyond Death | 332 | Rare | $0.49 | $0.99 |
4 rulings from Wizards of the Coast
- 24 January 2020If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 24 January 2020If all six of the revealed cards are land cards, your opponent doesn’t exile anything. You put all six cards into your hand.
- 24 January 2020If you cast a spell “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, such as that of Thrill of Possibility, those must be paid to cast the card.
- 24 January 2020If your opponent wishes to cast the card, they do so as part of the resolution of Allure of the Unknown. They can’t wait to cast it later. Timing permissions based on a card’s type are ignored.