Plague Boiler is a rare Artifact card from Ravnica: City of Guilds (RAV), collector number 269. Current market price: $0.26 (foil $1.41), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, put a plague counter on this artifact. {1}{B}{G}: Put a plague counter on this artifact or remove a plague counter from it. When this artifact has three or more plague counters on it, sacrifice it. If you do, destroy all nonland permanents.