Sea Dwarf
Okay, you sail around the lighthouse. Like I said, all is quiet, nothing of note except for the blue knight standing guard at the door.
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As for the stuff on the sea floor... uh, it's out to sea, and on the sea floor. 'Swimming' isn't the prof you want. A few classes at the Bayville Community Pool doesn't turn you into Cousteau. It's probably 100 feet down in choppy ocean water.
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The captain's name is Handsome Jack, and he's got a crew of four Sea Dwarfs. Like dwarves, but they're blue with sea green hair and they ride manatees and shit like Aquaman.