Diseased Vermin is a uncommon Creature — Rat card from Alliances (ALL), collector number 46. Current market price: $0.31, TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, put an infection counter on it. At the beginning of your upkeep, this creature deals X damage to target opponent previously dealt damage by it, where X is the number of infection counters on it.