Apocalymon
Apocalymon is essentially the Digital World's dumping ground—a massive repository of data from dead and unrevived digimon. What makes it unusual is that it's dominated by whatever digimon happens to be the largest and most powerful at any given moment. When the Chosen Children defeated the Dark Masters, those four ended up absorbed into Apocalymon, making it an even more formidable threat.
The thing that sets Apocalymon apart from typical "destroy everything" villains is that it actually has a coherent motivation. It harbors a deep resentment toward both the Children and the Digital World's entire system—one that it sees as fundamentally rigged, forcing digimon to conform or perish regardless of their nature. You could think of Apocalymon as a kind of collective consciousness of all the creatures (digital or otherwise) that lost out in the natural order, and it's angry about a world designed to crush them. That's a more interesting reason to want to burn it all down than most villains get.
Content compiled by AnimeList.moe from publicly available sources.
