Armor of Thorns is a common Enchantment — Aura card from Mirage (MIR), collector number 206. Current market price: $0.14, TCGplayer market prices via Scryfall.
You may cast this spell as though it had flash. If you cast it any time a sorcery couldn't have been cast, the controller of the permanent it becomes sacrifices it at the beginning of the next cleanup step. Enchant nonblack creature Enchanted creature gets +2/+2.