Cheapest priced copy (Oath of the Gatewatch): $0.35 at Card Kingdom, near mint, their price list as of .
Natural State 
Instant · Common · Oath of the Gatewatch · #136
Destroy target artifact or enchantment with mana value 3 or less.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Oath of the Gatewatch | 136 | Common | $0.35 | $1.49 |
One ruling from Wizards of the Coast
- 22 January 2016If an artifact or enchantment on the battlefield has {X} in its mana cost, X is 0.