Cheapest priced copy (Adventures in the Forgotten Realms): $0.49 at Card Kingdom, near mint, their price list as of .
Asmodeus the Archfiend 
Legendary Creature — Devil God · 6/6 · Rare · Adventures in the Forgotten Realms Promos · #88p
Binding Contract — If you would draw a card, exile the top card of your library face down instead.
{B}{B}{B}: Draw seven cards.
{B}: Return all cards exiled with Asmodeus to their owner's hand and you lose that much life.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $42.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 88 | Rare | $0.49 | $0.79 |
| Adventures in the Forgotten Realms | 373 | Rare | $0.69 | $2.99 |
| Adventures in the Forgotten Realms Promos | 88a | Rare | — | $42.99 |
| Adventures in the Forgotten Realms Promos | 88p | Rare | $2.49 | $1.99 |
| Adventures in the Forgotten Realms Promos | 88s | Rare | — | $5.99 |
3 rulings from Wizards of the Coast
- 23 July 2021If a card is exiled face-down and no player has been given permission to look at it, no player is allowed to look at it as long as it remains exiled face-down.
- 23 July 2021If your library is empty, no cards will be exiled but you won't lose the game due to drawing from an empty library.
- 23 July 2021If Asmodeus the Archfiend leaves the battlefield before you activate its last ability, any cards exiled by its replacement effect remain exiled face down for the rest of the game. If you somehow return the same Asmodeus the Archfiend card to the battlefield, it will be a different object with no connection to those face-down cards.