Gixian Skullflayer is a common Creature — Phyrexian Human Assassin card from The Brothers' War (BRO), collector number 100. Current market price: $0.17 (foil $0.21), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, if there are three or more creature cards in your graveyard, put a +1/+1 counter on this creature.