Ghost Pirates of the Sea-erra Madre

You swim up to the large glowing cube and, despite the skeletons of countless sea creatures littering the ocean floor, place your hand on its surface. You can feel the warmth of the cube radiating through your gloved hand.

You attempt to remove your hand from the cube, but find that you can't. You quickly realize that not only is your hand stuck to the cube, but it is being gradually pulled inside! You pull against it with all of your might, but nothing you do seems to be able to stop the slow, inexorable pull of the cube.

You can't see what's inside the cube, but it can't possibly be good, can it?

Looking around to see if there's anything nearby that could help, you spot an ancient looking cutlass lying inside the skeleton of a shark. You are just barely able to pull the sword within reach and grasp it by its handle. The sword still seems surprisingly sharp, but your attempts to cut or damage the cube lead to naught.

You could use the sword to cut off your arm before its fully absorbed by the cube or you could wait and hope that whatever's inside the cube will be safe. Your arm has been absorbed almost up to the elbow, so if you're going to do anything, you better do it soon!