Apocalymon and Diaboromon:

Attacks: Darkness Zone/ Big Bang/ Death Claw/ Virus Grenade/ Total Annihilation
When the Digidestined were brought to the Digital World they were brought for the purpose of fulfilling their destiny. But it wasn't until the very last two episodes of Season One that we learned just what horror had befallen the Digital World, Apocalymon. This Digimon was unlike any other, a Digimon that had invaded the Digital World from the outside and had begun corrupting the system. He was formed from all of the Data left over when Digimon had. All he had known his entire lifetime was pain and suffering caused by these losses and it had made his heart black with no room for fun or love or anything good. He had been defeated by the very first Digidestined from about 1970-1980, when he came out of the Ring of Fire that Gennai told the season 1 Digidestined about. However like Myotismon, he was not completely destroyed and rebuilt using the Data left over from Digivolving. When faced with the Digidestined, he mocked them and told them how he had been waiting for this day, the day that he could finally destroy them and their prophecies. He started with their tags, ripping them away and destroying them while devolving their Digimon back to base forms, tearing all hope from the kids of being able to stop them. After all, without tags, how could they Digivolve. But the Digidestined were chosen so because they didn't need the tags and crests to help their Digimon Digivolve. They had the power within. And when they finally realised it and worked together as a team, not even Apocalymon could stop them. This contradicts what happens in season 2 as the Digidestined use their tags and crests to seal away the evil and help the Digi-Guardians, this means they cannot Digivolve? This Digimon is officially listed as 'Unidentified' in Level, Kind, and Type.