Thraximundar is a mythic Legendary Creature — Zombie Assassin card from Alara Reborn (ARB), collector number 113. Current market price: $2.00 (foil $24.14), TCGplayer market prices via Scryfall.
Haste Whenever Thraximundar attacks, defending player sacrifices a creature of their choice. Whenever a player sacrifices a creature, you may put a +1/+1 counter on Thraximundar.