Cyclopean Tomb

{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.

30th Anniversary Edition

Masters Edition IV

{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 this ability only during your upkeep.
When Cyclopean Tomb 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 Cyclopean Tomb but that a mire counter has not been removed from with Cyclopean Tomb.

Collectors' Edition

Intl. Collectors' Edition

Will not add or remove the supertype snow to or from a land.

The delayed triggered ability created when Cyclopean Tomb is put into a graveyard from the battlefield triggers during each of your upkeeps for the rest of the game. As it resolves, you must remove a mire counter from a land that had a mire counter put on it by that instance of Cyclopean Tomb, but it doesn't matter where the mire counter you remove came from. For instance, you could remove mire counters that were put on the land by Gilder Bairn.

The land remains a Swamp as long as it has a mire counter on it. This effect is not tied to the Tomb remaining on the battlefield.