Cheapest priced copy (Mirrodin Besieged): $0.35 at Card Kingdom, near mint, their price list as of .
Mirran Mettle 
Instant · Common · Mirrodin Besieged · #84
Target creature gets +2/+2 until end of turn.
Metalcraft — That creature gets +4/+4 until end of turn instead if you control three or more artifacts.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 84 | Common | $0.35 | $0.49 |