Armageddemon

Armageddemon is an Unidentified Digimon whose name is derived from Armageddon, the location of the final battle between good and evil prophesied in the Bible. Armageddemon is a large, evil Digimon created when an enormous number of Kuramon fused into a giant Digi-Egg.

Digimon Tamers: Brave Tamer
An Armageddemon is in ZeedMillenniummon's party.

The Armageddemon card, titled "Armageddon Fire", is a Rank 6 card which teaches the Armageddon Fire technique. Armageddon Fire deals Virus-type damage to all enemies.

Digimon Savers 3D: The Digital World in Imminent Danger!
Armageddemon is absorbing Digital World's data via a black hole but is defeated through the efforts of Calumon, GeoGreymon, and Gaogamon.

Digimon World 3
Armageddemon appears in the opening video, and can be fought near the end of the game. Excluding five rare Digimon cards Armageddemon is the second strongest Digimon card after Imperialdramon Paladin Mode. Armageddemon is a black Mega Digimon card that has 65/62. Also, in the PAL version of the game, it is the third Digimon Kurt has.

Digital Monster D-Project
Armageddemon digivolves from MetalTyrannomon.

Digimon World DS
Armageddemon appears as a boss which makes up 2 zones, guarding the warp to the final boss, Chronomon Destroyer Mode.

Digimon World Dawn/Dusk
Armageddemon is obtainable through the DNA Digivolution of Diaboromon and Infermon, but you must also have a Kuramon in your party. You also have to have them at level 81 or higher, and a defense that is 480 or higher. After completing the main game, Armageddemon can be found in a single room at the end of the Magnet Mines (they can appear in somewhat-large numbers but can only be found in that one room). It is the strongest Digimon that is found in the wild in Dusk (they are especially dangerous when encountering in groups).

Attacks
 * Destiny Destroyer (Ultimate Flare): Fires a solar-hot energy blast from his mouth.
 * Full Scale Attack (Black Rain): Launches a swarm of missile-like projectiles from his back.

Trivia
For some unknown reason, Armageddemon's name was never mentioned in the Dub version of Revenge of Diaboromon.