You and a friend were deep sea diving with scuba tanks, which was great.

How so? You had to teach your friend how to scuba dive.

Flashes of a fin got you worried, and thinking it was a shark, you got your friends back up then headed after.

But, you were suddenly yanked down, and found yourself facing a mostly scaled...either merman or siren.

The tether that connected you to the boat also snapped, leaving you down here with limited air.

You..?

{{got this idea in the pool-