Swarmyard Massacre is a rare Sorcery card from Bloomburrow Commander (BLC), collector number 55. Current market price: $5.31, TCGplayer market prices via Scryfall.
Create two 1/1 green Squirrel creature tokens. Then each creature that isn't an Insect, Rat, Spider, or Squirrel gets -1/-1 until end of turn for each creature you control that's an Insect, Rat, Spider, or Squirrel.