"A fallen angel-type Digimon in the form of a gigantic male goat. It is a being of darkness born from the residual thought data of Apocalymon, who sought to annihilate all life. Its motive is the same as Apocalymon's: the annihilation of all life. It excels at dark magic and has an extremely cruel personality. However, it is highly intelligent and a strategist. Its signature move, "Black Sabbath," is a dark incantation that prays for a festival of death. Anyone who hears this incantation will soon die. Its ultimate attack is "Death Cloud," which generates a dark cloud that corrodes everything in its path."

Mephismon is 4 meters tall normally but he also can grow to be 30 meters tall. His main objective is to exterminate all living beings, but soon grown to enjoy playing with them first, break them and then consider to kill, or just keep as a stress toy or even as food.