If I play sundering titan and I hit an opponents island(I used spreading seas), is my own snow islands safe or do I lose one?I say no,that a basic island is a basic island whether it's snow or not.
Any land with a basic land type can be chosen for Sundering Titan's ability (for example, a land that's currently an Island due to Spreading Seas); it doesn't matter what supertypes the land has (such as basic or snow [C.R. 205.4a]) (C.R. 608.2h). If only you control a land of a particular basic land type, however, you must choose it.
You choose a (meaning one) land of each basic land type. If you choose an island an opponent controls, the Titan won't do anything to any of your islands.
There are five land subtypes that are known as 'basic land types': plains, island, swamp, mountain, and forest ("snow" is a supertype, not a land type). You will choose exactly one land that has the subtype plains, one island, one swamp, one mountain, and one forest (unless there is no land of that type on the battlefield to be chosen, of course), so the Titan will destroy, at most, five lands.
The Titan doesn't destroy all islands or even all basic islands or anything like that. Just one land of each basic type.
Your Snow-Covered Island is safe because you already chose one island. If there were no other island, you'd be forced to choose the snow one to be destroyed.
There are five land subtypes that are known as 'basic land types': plains, island, swamp, mountain, and forest ("snow" is a supertype, not a land type). You will choose exactly one land that has the subtype plains, one island, one swamp, one mountain, and one forest (unless there is no land of that type on the battlefield to be chosen, of course), so the Titan will destroy, at most, five lands.
The Titan doesn't destroy all islands or even all basic islands or anything like that. Just one land of each basic type.
Your Snow-Covered Island is safe because you already chose one island. If there were no other island, you'd be forced to choose the snow one to be destroyed.