If you and a permanent you control each become the targets of the same spell or ability an opponent controls, Unsettled Mariner’s ability will trigger twice. The same is true if two permanents you control each become the targets of the same spell or ability an opponent controls.

If a spell or ability an opponent controls targets only you or only one permanent you control, but it targets you or that permanent multiple times, Unsettled Mariner’s ability triggers only once.