Cheapest priced copy (Adventures in the Forgotten Realms): $0.49 at Card Kingdom, near mint, their price list as of .
Sphere of Annihilation 
Artifact · Rare · Adventures in the Forgotten Realms · #121
This artifact enters with X void counters on it.
At the beginning of your upkeep, exile this artifact, all creatures and planeswalkers with mana value less than or equal to the number of void counters on it, and all creature and planeswalker cards in graveyards with mana value less than or equal to the number of void counters on it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.49 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 121 | Rare | $0.49 | $0.49 |
| Adventures in the Forgotten Realms | 376 | Rare | $0.59 | $0.49 |
| Adventures in the Forgotten Realms Promos | 121a | Rare | — | $5.99 |
| Adventures in the Forgotten Realms Promos | 121p | Rare | $0.49 | $0.49 |
| Adventures in the Forgotten Realms Promos | 121s | Rare | — | $0.69 |
One ruling from Wizards of the Coast
- 23 July 2021If a permanent on the battlefield or a card in a graveyard has {X} in its mana cost, X is 0 when determining that card's mana value.