When Sundering Titan enters the battlefield or leaves the battlefield, choose a land of each basic land type, then destroy those lands.
12/1/2004 Sundering Titan’s two abilities aren’t targeted. When one of the abilities resolves, the Titan’s controller must choose one land for each basic land type (Plains, Island, Swamp, Mountain, and Forest).
12/1/2004 If one of the basic land types isn’t present, it isn’t chosen. If the only land of a certain type is one you control, you must choose it.
12/1/2004 If a land has more than one basic land type, it can be chosen more than once.
12/1/2004 All the chosen lands are destroyed simultaneously.