Cloudhoof Kirin is a rare Legendary Creature — Kirin Spirit card from Saviors of Kamigawa (SOK), collector number 31. Current market price: $0.52 (foil $3.64), TCGplayer market prices via Scryfall.
Flying Whenever you cast a Spirit or Arcane spell, you may have target player mill X cards, where X is that spell's mana value.