Cheapest priced copy (Journey into Nyx): $0.35 at Card Kingdom, near mint, their price list as of .
Nightmarish End 
Instant · Uncommon · Journey into Nyx · #76
Target creature gets -X/-X until end of turn, where X is the number of cards in your hand.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Journey into Nyx | 76 | Uncommon | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 26 April 2014The value of X is calculated as the ability resolves. The effect won't change later in the turn, even if the number of cards in your hand does.