Legendary Land Each land is a Swamp in addition to its other land types. "Yawgmoth's corpse is a wound in the universe. His foul blood seeps out, infecting the land with his final curse." —Lord Windgrace
Illus. John Avon
2/1/2007: Urborg is not a Swamp while it's not on the battlefield.
2/1/2007: While it is on the battlefield, Urborg is a Swamp and thus has the ability "{T}: Add {B} to your mana pool."
2/1/2007: If Urborg loses its abilities (for example, it becomes a creature and then Ovinize is cast on it), all lands on the battlefield, including Urborg, will still be Swamps, but Urborg won't have the ability "Each land is a Swamp in addition to its other land types." Urborg also won't be able to tap to produce {B}, but other lands (including those that enter the battlefield later in the turn) will. The way continuous effects work, Urborg's type-changing ability is applied before Ovinize removes both the type-changing ability and its own mana ability.
2/1/2007: This is not the same card as the Legendary Land Urborg from the Legends set. Both of them can be on the battlefield at the same time.
4/1/2008: If Urborg, Tomb of Yawgmoth and either Blood Moon or Magus of the Moon are on the battlefield, all nonbasic lands will be Mountains, not Swamps. Urborg, Tomb of Yawgmoth will be a Mountain as well. It will have "{T}: Add {R} to your mana pool" and no other abilities.
Planar Chaos
(Rare)