Karumonix, the Rat King is a rare Legendary Creature — Phyrexian Rat card from Phyrexia: All Will Be One Promos (PONE), collector number 98s. Current market price: — (foil $6.48), TCGplayer market prices via Scryfall.
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.) Other Rats you control have toxic 1. When Karumonix enters, look at the top five cards of your library. You may reveal any number of Rat cards from among them and put the revealed cards into your hand. Put the rest on the bottom of your library in a random order.