Cheapest priced copy (Magic 2011): $0.35 at Card Kingdom, near mint, their price list as of .
Primal Cocoon 
Enchantment — Aura · Common · The List · #M11-191
Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.
When enchanted creature attacks or blocks, sacrifice this Aura.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Magic 2011 | 191 | Common | $0.35 | $0.49 |
| The List | M11-191 | Common | $0.35 | — |
2 rulings from Wizards of the Coast
- 15 August 2010The counters are put on the creature, not on Primal Cocoon. They'll stay on the creature even after Primal Cocoon is sacrificed or otherwise stops enchanting that creature.
- 15 August 2010Primal Cocoon's first triggered ability triggers at the beginning of the upkeep of Primal Cocoon's controller (who is not necessarily the enchanted creature's controller).