Cyclopean Tomb is a rare Artifact card from 30th Anniversary Edition (30A), collector number 533. Current market price: $138.30, TCGplayer market prices via Scryfall.
{2}, {T}: Put a mire counter on target non-Swamp land. That land is a Swamp for as long as it has a mire counter on it. Activate only during your upkeep. When this artifact is put into a graveyard from the battlefield, at the beginning of each of your upkeeps for the rest of the game, remove all mire counters from a land that a mire counter was put onto with this artifact but that a mire counter has not been removed from with this artifact.