The Plate of Pearl (ca. 2700 BC)
When Arceus's meteor shattered, one of its plates fell deep into the Baltic Sea and into the stomach of a giant mollusk, one of the ancestors of modern cloyster. The creature was far too weak to withstand the power within the plate, so it killed the mollusk's body rather than transforming it - but not before the mollusk had attempted to fight off the irritant by secreting a protective liquid. As the mollusk died, this liquid coated the plate and encased it in a beautiful, pearlescent sheen.
In the next ten thousand years, the lustrous plate sat on the ocean floor, attracting fish and other creatures with its shine and killing them when they strayed too close. Its power was not one of fire or electricity, but one of spatial distortion. It killed by slowly twisting atoms and molecules, disfiguring one's body so that it died sometimes slowly, but often quickly. Thus, over time, it was buried under sediment and animal remains, forgotten to the world.
On the shores of this Baltic Sea, circa 2700 BC, lived a clan of amphibious dragons. These dragons were the ancestors of modern garchomp. Before the so-called "land shark" evolved to dwell upon dry earth, its ancestors possessed fins much more suitable for swimming, and pale coloration which helped them camouflage in the icy waters of the North.
Palkia was a member of this species, and one of their most adept swimmers. She loved the thrill of flying through water, competing with the ancestors of gyarados and sharpedo to achieve the most blistering speeds. She often looked toward the sky, however, envying the birds which flew so freely. Her species' large dorsal fins resembled wings, but were wholly unsuitable for true flight.
During her early adulthood, Palkia entered a battle with a school of enormous megafish - ancestors of today's gyarados - which had threatened to devour her little hatchlings. Normally, she could fend off one of these with little trouble, but this time, her family had run afoul of five at once. The battle was quick and decisive, with all of her children killed. Palkia was rammed into the ocean floor, broken and bloody, though her attackers let her be once they had eaten their fill of her little ones.
It was many months before she recovered fully, and her family had long since disappeared. After she regained her strength, she noticed a glint in the sand where she had lay wounded. In the rush of battle, the sediment in the ocean floor had been kicked up, disturbing decades of animal bones, and revealing one fascinating, shining plate.
Curiously, and without anything to lose, Palkia touched the pearlescent plate with one hand.
Just as with Dialga only one century before, Palkia's body was immediately paralyzed. The plate filled her bloodstream with its godly power, and due to the strength of her body and mind, it did not kill her, though it forced her into a decades-long coma. The plate dissolved quickly into her body, enlarging her muscles and thickening her sinews, expanding her dorsal fins until they indeed resembled wings, and rendering her immortal.
Perhaps most importantly at all, the plate filled her bloodstream with the power of space. Or, to be more specific, receptors that could feel the fabric of space. When Palkia awoke from her bewildering sleep, she not only felt the twisting, flowing pull of seawater around her, but she felt the undeniable pull of a second ocean: the ocean of space, of atoms and molecules around and within her, floating in an eternal plane that would be hers to claim.