Fraying Sanity is a rare Enchantment — Aura Curse card from Hour of Devastation (HOU), collector number 35. Current market price: $0.70 (foil $1.34), TCGplayer market prices via Scryfall.
Enchant player At the beginning of each end step, enchanted player mills X cards, where X is the number of cards put into their graveyard from anywhere this turn.