Pestilence Rats is a common Creature — Rat card from Ice Age (ICE), collector number 157. Current market price: $0.30, TCGplayer market prices via Scryfall.
Pestilence Rats's power is equal to the number of other Rats on the battlefield. (For example, as long as there are two other Rats on the battlefield, Pestilence Rats's power and toughness are 2/3.)