Apocalymon

Apocalymon is a massively powerful digimon that takes the form of a giant polyhedron, with a comparitively tiny humanoid being resembling Devimon coming from the top. Filled with dark thoughts, Apocalymon was born from the assimilated data of every Digimon that failed to evolve. Apocalymon's arrival was written down in ancient prophecies and the hatred of the Digimon that formed him lingered on. A sadistic and tormented soul, Apocalymon wanted to make the Digital World a living hell to justify the darkness that composes him. He knows all the evolutions and attacks of Digimon. In contrast to English version, the Japanese version had Apocalymon refer to himself in the plural sense. There are two possible reasons for this: he had no one to talk to but himself in his void-like dimension; or as a reference to the demon Legion who was also composed of many. Thus from the 2nd reason, Apocalymon, as a being assembled from the data of thousands if not millions of digimon, may truly had been a plural entity.

Attacks

 * Grand Death Big Bang (Total Annihilation): Suicide attack that produces an explosion strong enough to wipe out an entire dimesion. Used as a final resort.
 * Death Evolution (Reverse Digivolve): Reverts Digimon.
 * Darkness Zone: Reverts his enemies to nothingness.
 * Virus Grenades: Launches laser grenades at his opponents.
 * Copied attacks: The giant claws morph to enable Apocalymon to use the attacks of others.
 * Mugen Cannon (Giga Cannon): Machinedramon's attack
 * Ulitmate Stream (River of Power): MetalSeadramon's attack.
 * Bloody Stream (Crimson Lightning): Myotismon's attack.
 * Death Claw (Touch Of Evil): Devimon's attack. Can send a lot of Devimon arms to seize opponents.

Digimon Adventure
Revealed to be reponsible for creating the chaos in the Digital World, Apocalymon appeared to destroy the DigiDestined with his powers. He destroyed the Tags and Crests and sent the DigiDestined to the Data World before they returned using the "Crest" power that was within them all along. It took a combined force of WarGreymon, MetalGarurumon, Garudamon, MegaKabuterimon, Lillymon, Zudomon, MagnaAngemon and Angewomon to even begin to harm him; during their battle they managed to destroy the humanoid portion of him. However, as he explained, the humanoid form was only a part of him, albeit an important one. A dying Apocalymon then attempted to take the DigiDestined down with him using his ultimate attack, Total Annihilation. However, the digivices of the Digi-destined contained and negated this kamikaze attack.

Digimon Tamers
What might be Apocalymon was among the shadowed Digimon that wanted Rika to tame one of them.

The Adventurer's Battle
Apocalymon attempted to cross into the Real World to destroy it until he was confronted by Omnimon. But when he was seemingly killed by Omnimon, Apocalymon's data reformed into a new evil to carry out his justice. Its name was Mephistomon.

Digimon Adventure, Dub

 * I know who you are! You don't have the power to eliminate my sadness.
 * I am the ultimate evil, complete with hot and cold running water.
 * Are you repulsed by my appearence?
 * Don't be afraid to hurt my feelings. They're already hurt. You see, I was created from all that was lost during the digivolving process.
 * Digimon have been digivolving for many years now, over and over again. But there were some who weren't up to the challenge and simply disappeared.
 * Silence! Who's the one telling the story anyway, me or you?
 * First I have a question to ask. Do you believe that I am worthy of coexisting with you?
 * Oh really? Even though I was forged from the pain and misery of all the elvated Digimon who vanishing while attempting to digivolve.
 * Sure, rub it in. And now DigiDestined and Digimon. I have been waiting a eternity for this encounter.

Digimon Adventure, Original

 * Are we not worthy of being with others!? Answer us!
 * HAHAHAHAHA! Let all the light shines on be no more!