"Ahh, isn't that the question," Buffet said with a wistful sigh. "Humans... They are both the strongest and weakest species, in a way. Despite their lack of individual strength, they always seem to dominate the biomes that they enter, especially if they do so in great numbers. When the Dark Omen of the Bittercold had first arrived, I had assumed this and summoned as many humans as I possibly could to overwhelm it with sheer numbers. Unfortunately, well... I was wrong. Only some humans have this talent, and I knew to search more carefully next time. I do wonder if your Dark Matter had a similar philosophy, or if he tried what I had, and got as much as he could...
"Right, humans. Sorry! Distracted. Humans are unique in the kingdom of life because of the way their energy interacts with Pokemon. Humans are not strong, but they strengthen their Pokemon allies--both in terms of raw power, and growth. This power originates not in their bodies, but their spirits... And so, that is all I need to bring over.
"So then, what happens if you wrap a human spirit in a Pokemon body? You get something that is... truly powerful. Something that can oppose the gods themselves... to an extent." Buffet giggled. "They have their limits, but for the purpose of calming a god, or felling one that was already weakened and corrupted, much like what you're doing now? It is certainly enough.
"But that sort of power is risky. I have to select humans very carefully, and, for a while, the decision was that once a human's duty was complete, they would be forced to return home. Humanity would send this world off its balance of power, or at least change the status quo. And gods tend to be averse to changing things unnecessarily. Though"--Buffet lowered his voice to a whisper--"they probably should. Arceus took far too long to modernize his language, and I think he misfired the era when he tried.
"Anyway!" Back to normal. "That's the gist of it. Finding a human is the base need to conquer a problem we cannot easily handle on our own. You know, I once heard a story about a human who had tried to become the next Arceus in a world like this one, though I heard tell it did not end well... Hmm. But I suppose that's not important for here. It is interesting to think about, though. If one could summon an Arceus-human to assist... But then, well, they'd have their own responsibilities, wouldn't they?" He frowned, pensive. "And I do not know how to feel about a human Arceus. It seems... uncharted. Perhaps for the better."