The Black Demon Shark (Spanish: El Demonio Negro) is an enormous black shark whose territory is said to be just off the coast of Mexico's Baja California peninsula. In recent times, several local fishermen have reported seeing the black monstrosity. The Black Demon is said to be 20-60 feet long and weighing anywhere between 50-100,000 lbs! It is said to resemble a great white, but with very dark coloration and a truly monstrous tail.
Some say it could be the Megalodon or a new species of shark, maybe even an over sized Great White. Many expeditions were launched to locate this monstrous creature, even on MonsterQuest in the chapter Mega-Jaws, but they didn't discover anything. Sadly, sightings are rare and the creature is elusive. Because of this, not much is known. It is possible since albinism is found in sharks that melanism could be too.
Info from cryptid wiki, and this weeks cryptid was commissioned!