Apocalymon

Apocalymon is an evil Digimon. He is never seen in the series, only mentioned. He has the appearance of a large dodechahedron with claws and a humanoid form. He is beyond the Mega level.

Apocalymon intended to destroy the world, but was was destroyed, presumably by Omnimon. However, his data was reformatted into Mephistomon, who serves as antagonist of Battle of Adventurers.

Trivia

 * In the original series, Apocalymon is the final antagonist of Season 1 and the one behind the Dark Masters.
 * His name is derived from the word "apocalypse".