Elder Mastery is a uncommon Enchantment — Aura card from Duel Decks: Ajani vs. Nicol Bolas (DDH), collector number 68. Current market price: $0.37, TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature gets +3/+3 and has flying. Whenever enchanted creature deals damage to a player, that player discards two cards.