Cheapest priced copy (Mirrodin Besieged): $0.39 at Card Kingdom, near mint, their price list as of .
Viridian Corrupter 
Creature — Phyrexian Elf Shaman · 2/2 · Uncommon · Mirrodin Besieged · #94
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
When this creature enters, destroy target artifact.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.39 to $3.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 94 | Uncommon | $0.39 | $3.49 |
| Phyrexia: All Will Be One Commander | 113 | Uncommon | $0.99 | — |
2 rulings from Wizards of the Coast
- 1 June 2011If there are no artifacts on the battlefield when Viridian Corrupter enters the battlefield, its enters-the-battlefield does nothing. Viridian Corrupter will simply enter the battlefield.
- 1 June 2011The enters-the-battlefield ability is not optional. You must target an artifact you control if there are no other artifacts on the battlefield.