Mephistomon

Mephistomon is a Dark Animal Digimon whose name is derived from the fictional Mephistopheles and whose design is derived from the mythological Baphomet. It has the appearance of a giant ram, and is a dark being born from the lingering thought-data of an Apocalymon that attempted to destroy all life. Like Apocalymon, its governing principle is the extermination of all life. It specializes in the black magic of the Dark-species, and its personality is endlessly cruel. However, it is extremely intelligent, and is also a tactician.[2]

Digimon Tamers: Battle of Adventurers
Mephistomon is the main antagonist in the Digimon Tamers movie "Battle of Adventurers."

Reformatted from an Apocalymon, Mephistomon has a deep hatred for all life, and so plots to destroy the world and everything in it. In order to do so, he disguises himself as Ryuuji Tamashiro, the president of the Okinawan VP Laboratories. He soon becomes famous for his part in marketing the V-Pet, a digital pet that he modified to cause other Digimon to Bio-Emerge and become his servants.

Takahito Uehara, the original creator of the V-Pet, detects the virus that Mephistomon had implanted in the V-Pets, and creates a vaccine program which he implants into the original V-Pet, which manifests as Seasarmon. When Mephistomon finds out about the vaccine, he uses his servants to kidnap Takehito and find out the vaccine's location. Once Uehara reveals that the vaccine is in Seasarmon, Mephistomon doffs his disguise and attacks Seasarmon and the Tamers. As part of the battle, he drags the group into an apocalyptic dimension modeled after his intentions for the Real World. Even Mephistomon was stronger the Tamers' digimon (who fought in the their Champion forms), he was defeated by Growlmon blasting a ship floating in the sky, causing it to fall on him, allowing the vaccine program to activate and purge the virus. It is revealed that Mephistomon is not actually dead, and he digivolves to Gulfmon.

Role in Ultima
Attacks
 * Black Sabbath: Recites a dark incantation in which it prays for a festival of death; those who hear the spell soon die.
 * Dark Cloud (Death Cloud): Generates a cloud of darkness which causes everything to decay.