Hatchetfish are deep-sea fish found in the Pacific, Atlantic, and Indian oceans. They use a form of bioillumination to mimic light intensity from the surface, effectively cloaking it from poor-sighted predators. Creepy, but cool.
Despite its frightening appearance, the Sloane's viperfish (or Sloane’s fangfish) is a harmless to humans dragon fish of the Chauliodus genus. It can be found all over the world in tropical and subtropical oceans, living in very deep depths.