Void Winnower is a mythic Creature — Eldrazi card from Battle for Zendikar Promos (PBFZ), collector number 17p. Current market price: $39.64 (foil $50.96), TCGplayer market prices via Scryfall.
Your opponents can't cast spells with even mana values. (Zero is even.) Your opponents can't block with creatures with even mana values.