Cheapest priced copy (Rivals of Ixalan): $0.49 at Card Kingdom, near mint, their price list as of .
Sphinx's Decree 
Sorcery · Rare · Rivals of Ixalan · #24
Each opponent can't cast instant or sorcery spells during that player's next turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Rivals of Ixalan Promos | 24s | Rare | — | $1.49Out of stock |
| Rivals of Ixalan | 24 | Rare | $0.49 | $0.49 |
One ruling from Wizards of the Coast
- 19 January 2018If multiple effects say that an opponent can’t cast instant or sorcery spells during that player’s next turn, they all apply to the same turn.