Cheapest priced copy (Double Masters): $0.35 at Card Kingdom, near mint, their price list as of .
Corridor Monitor 
Artifact Creature — Construct · 1/4 · Common · Throne of Eldraine · #41
When this creature enters, untap target artifact or creature you control.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters | 46 | Common | $0.35 | $0.49 |
| Throne of Eldraine | 41 | Common | $0.35 | $0.49 |