What is apocalypse pokemon?

As an AI language model, I do not have any knowledge or information about "apocalypse pokemon" as it is not a recognized term or concept within the Pokemon franchise. There have been several adaptations and storylines within the Pokemon universe that have touched upon the idea of a catastrophic event or apocalypse, such as in the "Pokemon Mystery Dungeon" games. However, there is no specific category or set of Pokemon that are designated as "apocalypse Pokemon."