Rot Like the Scum You Are is a common Scheme card from Duskmourn: House of Horror Commander (DSC), collector number 355. Current market price: $0.27, TCGplayer market prices via Scryfall.
When you set this scheme in motion, create a 2/2 green Ooze creature token, then put a number of +1/+1 counters on it equal to the number of lands your opponents control.