Patron of the Nezumi is a rare Legendary Creature — Spirit card from Betrayers of Kamigawa (BOK), collector number 77. Current market price: $0.50 (foil $12.13), TCGplayer market prices via Scryfall.
Rat offering (You may cast this spell any time you could cast an instant by sacrificing a Rat and paying the difference in mana costs between this and the sacrificed Rat. Mana cost includes color.) Whenever a permanent is put into an opponent's graveyard, that player loses 1 life.