Relentless Rats is a special Creature — Rat card from Time Spiral Remastered (TSR), collector number 329. Current market price: $4.64 (foil $12.60), TCGplayer market prices via Scryfall.
This creature gets +1/+1 for each other creature on the battlefield named Relentless Rats. A deck can have any number of cards named Relentless Rats.