Szadek, Lord of Secrets is a rare Legendary Creature — Vampire card from Ravnica: City of Guilds (RAV), collector number 234. Current market price: $0.30 (foil $4.87), TCGplayer market prices via Scryfall.
Flying If Szadek would deal combat damage to a player, instead put that many +1/+1 counters on Szadek and that player mills that many cards.