Cheapest priced copy (Mirrodin Besieged): $0.59 at Card Kingdom, near mint, their price list as of .
Plaguemaw Beast 
Creature — Phyrexian Beast · 4/3 · Uncommon · Mirrodin Besieged · #87
{T}, Sacrifice a creature: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
2 printings · $0.59 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 87 | Uncommon | $0.59 | $0.99 |
| The List | TD2-62 | Uncommon | — | — |
2 rulings from Wizards of the Coast
- 1 June 2011You can sacrifice Plaguemaw Beast to pay the cost of its own activated ability.
- 1 June 2011You can activate the ability even if there are no players or permanents with counters on them.