Cheapest priced copy (Phyrexia: All Will Be One Commander): $2.29 at Card Kingdom, near mint, their price list as of .
Ichorclaw Myr 
Artifact Creature — Phyrexian Myr · 1/1 · Common · Scars of Mirrodin · #166
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever this creature becomes blocked, it gets +2/+2 until end of turn.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
2 printings · $2.29 to $13.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Phyrexia: All Will Be One Commander | 133 | Common | $2.29 | — |
| Scars of Mirrodin | 166 | Common | $2.29 | $13.99 |
7 rulings from Wizards of the Coast
- 1 January 2011The -1/-1 counters remain on the creature indefinitely. They're not removed if the creature regenerates or the turn ends.
- 1 January 2011Damage from a source with infect is damage in all respects. If the source with infect also has lifelink, damage dealt by that source also causes its controller to gain that much life. Damage from a source with infect can be prevented or redirected. Abilities that trigger on damage being dealt will trigger if a source with infect deals damage, if appropriate.
- 1 January 2011Whenever Ichorclaw Myr becomes blocked, its last ability triggers just once, no matter how many creatures it became blocked by. It will get just +2/+2.
- 1 January 2011A player who has ten or more poison counters loses the game. This is a state-based action.
- 1 January 2011If damage from a source with infect that would be dealt to a player is prevented, that player doesn't get poison counters. If damage from a source with infect that would be dealt to a creature is prevented, that creature doesn't get -1/-1 counters.
- 1 January 2011Damage from a source with infect affects planeswalkers normally.
- 1 January 2011Infect's effect applies to any damage, not just combat damage.