There are many stories about the beginning of our once-beautiful Earth. I'm here only to tell you the one I know. To pass down knowledge.
When the Earth was first formed, Arceus, who had hatched from a shell of pure light and grown from a drop of pure darkness, was all there was. The landscape was empty and monochrome. So, he created many powerful beings, which he dubbed demons, from his own blood whose sole meaning was to inhabit the world and make it habitable for weaker descendants.
He created sub-groups based off of attributes and elements, what we know today as types: Normal, Fire, Fighting, Water, Flying, Grass, Ink, Poison, Electric, Light, Ground, Psychic, Sound, Rock, Ice, Bug, Dragon, Ghost, Dark, Steel, Fairy, and a small group known only as Man.
These beings, all created and shaped to the will of their own minds, their strengths and weaknesses embodied, arose from the inky, frothing sea and populated the barren Earth, by their own powers breathing oxygen and thus life onto the world.
But unrest was in the air from the start, saturated and drifting over the heads of the now meek Pokemon who had forced themselves to get rid of their more prominent powers for the sake of a peaceful lifestyle. A need for dominance had seeped into their minds. The cunning slaughtered the wary, some even killing their own kind in an attempt to establish dominance and create a strict hierarchy based off of natural selection. The land was dyed red with the blood of the innocent.
This self-destructive nature caused the extinction of many of the original beasts over time. Sound, light and ink were eliminated non-ceremoniously by the choking hold of pride, leaving the malice-driven fire, darkness and man and the well-meaning types in their wake. But even the soft hearted were not without it's cruel instincts. They killed to survive, to feed off of the corpses of their elders and to hoard their prey for themselves.
But a self-saving hero arose in the form of man. They quickly became self aware of their own intelligence and began developing languages of their own, dividing themselves into cultures and beating down the other Pokemon in order to have their power known. They blocked out other creatures and created a plastic utopia in order to make it seem like all was right, raising their kin peacefully. Some even dared to tame and breed the Pokemon, creating mindless monsters that were pit against each other for show.
Rebellion was brewing, and it continued doing so for years, hatred festering between all animalistic Pokemon as they were forced to scavenge and bow down to the humans who stabbed them for fun and for their pelts. The dark and fire reluctantly joined with the other elementals and types, having to tone down their violent instincts for the sake of a well-executed plan.
They sacrificed themselves to the humans, letting themselves die pitiful deaths. It was all just a part of setting up a masque, an illusion of weakness.
But the time for revenge had finally fallen upon them. All of them were few in number, and the weaker had been hacked off the Earth and into the dreamscape.
And so it ended as it began - violently. The beasts had inherited the Earth, snatching it from the hand that fed them. They snapped power from the throats of humans with a quick jerk and a metallic clip of their teeth.
The end was surely near.