Cheapest priced copy (Battlebond): $0.35 at Card Kingdom, near mint, their price list as of .
Noxious Dragon 
Creature — Dragon · 4/4 · Uncommon · Fate Reforged · #77
Flying
When this creature dies, you may destroy target creature with mana value 3 or less.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
5 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battlebond | 152 | Uncommon | $0.35 | $0.49 |
| Commander Legends | 139 | Uncommon | $0.35 | $0.49 |
| Fate Reforged | 77 | Uncommon | $0.35 | $0.49 |
| Iconic Masters | 100 | Uncommon | $0.35 | $0.49 |
| The List | FRF-77 | Uncommon | $0.35 | — |
2 rulings from Wizards of the Coast
- 24 November 2014A face-down creature has a mana value of 0. However, its mana value changes when it's turned face up. Thus, if a creature is turned face up in response to being targeted by Noxious Dragon's ability, it may become an illegal target.
- 10 November 2020If a creature on the battlefield has {X} in its mana cost, X is considered to be 0.