Oona's Blackguard is a uncommon Creature — Faerie Rogue card from Jumpstart (JMP), collector number 261. Current market price: $0.40, TCGplayer market prices via Scryfall.
Flying Each other Rogue creature you control enters with an additional +1/+1 counter on it. Whenever a creature you control with a +1/+1 counter on it deals combat damage to a player, that player discards a card.