When Sundering Titan enters the battlefield or leaves the battlefield, choose a land of each basic land type, then destroy those lands.
3/16/2018 Sundering Titan’s ability isn’t targeted. When it resolves, Sundering Titan’s controller must choose one land for each basic land type (Plains, Island, Swamp, Mountain, and Forest), and then they are destroyed simultaneously.
3/16/2018 Players can’t take actions in between the time you choose the lands and the time you destroy them. Notably, they can’t activate mana abilities of those lands.
3/16/2018 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.
3/16/2018 If a land has more than one basic land type, it can be chosen more than once.