Serra Advocate is a uncommon Creature — Angel card from Duel Decks Anthology: Divine vs. Demonic (DVD), collector number 7. Current market price: $0.45, TCGplayer market prices via Scryfall.
Flying {T}: Target attacking or blocking creature gets +2/+2 until end of turn.
All Duel Decks Anthology: Divine vs. Demonic cards and prices