Nefarox, Overlord of Grixis is a rare Legendary Creature — Demon card from Magic 2013 (M13), collector number 103. Current market price: $0.36 (foil $0.44), TCGplayer market prices via Scryfall.
Flying Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.) Whenever Nefarox attacks alone, defending player sacrifices a creature of their choice.