Withering Hex is a uncommon Enchantment — Aura card from Onslaught (ONS), collector number 181. Current market price: $0.21 (foil $0.41), TCGplayer market prices via Scryfall.
Enchant creature Whenever a player cycles a card, put a plague counter on this Aura. Enchanted creature gets -1/-1 for each plague counter on this Aura.