Cheapest priced copy (Conspiracy: Take the Crown): $0.35 at Card Kingdom, near mint, their price list as of .
Opaline Unicorn 
Artifact Creature — Unicorn · 1/2 · Common · Theros · #218
{T}: Add one mana of any color.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Conspiracy: Take the Crown | 213 | Common | $0.35 | $0.99 |
| Theros | 218 | Common | $0.35 | $0.79 |