Primal Cocoon is a common Enchantment — Aura card from Magic 2011 (M11), collector number 191. Current market price: $0.19 (foil $0.40), TCGplayer market prices via Scryfall.
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.