As the party moves towards the figure on the beach, it moves away, with a shuffling, shambling gait. It seems unused to walking on land. At the water's edge, the figure doesn't hesitate for a second before wading into the ocean. Just as the figure gets knee-deep into the water, the light from the lighthouse flashes around, illuminating the scene properly.
You see that the figure is a naked fish-like humanoid, with bulging eyes, clawed hands, and scaly green-black skin. The creature is carrying a strange stone idol under its arm, which depicts some kind of weird deep-sea fish, looks like a mix between a gulper eel and an angler fish. As you watch, the creature quickly gets waist-deep, then chest-deep into the crashing surf, before disappearing under the water entirely.
Looking at the boxes on the beach, they appear to be fairly mundane shipping crates. You could break them open if you wanted to look inside.
What do you want to do from here?