When Sundering Titan comes into play, choose a land of each basic land type, then destroy those lands.
When Sundering Titan leaves play, choose a land of each basic land type, then destroy those lands.
Let me just explain this and see if I am understanding this correctly. All this is assuming that I am playing the Titan.
1) I must pick a plain, forest, island, mountain, and swamp. If there is no plains, for example, then obviously no land for that type can be chosen.
2) My opponent has only a Volcanic Island, I can choose the same land for both the mountain and island to protect my own lands.
3) My opponent has only a Volcanic Island and I have an Underground Sea, then I must choose my Underground Sea as the swamp to destroy.
