Hey guys, this is my first oneshot and crossover. I got this idea off of a Youtube comment that explains how Pokémon were created in similar manner to what's written below, but I decided to elaborate a bit more on it.
Many have wondered how Pokémon came to exist. There is one legend that tells all of this, and I shall share it with you folks who are reading this.
Back then, there was a young PSI user that some of us may or may not know – Lucas. Lucas was once assigned a mission to pull the Seven Needles that sealed away the Dark Dragon under the Nowhere Islands. The only person who opposed this was Porky Minch (also known as Pokey Minch to some). After a desperate race against time, Lucas succeeded his mission when he pulled out the final Needle.
The Needle awakened the Dragon and responded to Lucas' wish of protecting all life in the world. Porky's chimeras were spared and they roamed free around the land. Peace came onto the land for a long while.
Millenniums passed. During that time, the chimeras as well as PSI underwent a drastic evolution. The people who still remembered Lucas' legend called the chimeras Porky/Pokey Monsters, or Pokémon for short. The name stuck with the people who never knew about the legend. The Pokémon moves that we know today are actually evolved forms of PSI. PSI had split types to create Grass, Water, Dark, Psychic, Steel, Dragon, Rock, Flying, Bug, Normal, Ghost, Poison, Fighting, and Fairy.
There were some people who were able to read the thoughts and feelings of Pokémon. They are, in reality, descendants of human PSI users. The population of human PSI users dropped drastically over the thousands of years due to human nature with humans being selfish and forcing Pokémon to do their bidding rather than doing it themselves, causing them to lose touch with PSI. Now, only Telepathy is available for these descendants.
At some point in time, people learned about Porky and the Absolutely Safe Capsule he used. They thought it was a great idea, and thus the Master Ball was created. Except they added on a latch so it wouldn't be impossible to get out once you get in.
The Unova legend mentioned that there were two twin brothers fighting over ideal and truth, and a dragon split into two to each support a side. This legend is not accurate. It is actually mentioning Lucas and his twin brother Claus' final battle for the final Needle. What really happened was that after Lucas died, the Dark Dragon could not keep his wish, as the heartless side of Claus plus his corrupted side began to take over it. As in result, it split into three dragons, which we now know as Zekrom, Reshiram, and Kyurem.
There were actually two twin Pokémon that were created in honor of Claus and Lucas. We know them as Latias and Latios. Latias, being a representation of Lucas, was originally intended to be male too, but the experiment had backfired and Latias came out as a female. But the scientists thought that Latias acted very similar to Lucas anyway, so they were like, it doesn't matter, let's just save time and energy and leave it at that.
There were a group of people who knew the origins of PSI as well as Ness and Ninten's fight against Giygas. They were known as Team Rocket, and they attempted to recreate Giygas as accurately as possible. Since they required Mew's cells, they called it Mewtwo rather than Giygas, because they knew that they couldn't perfectly emulate Mewtwo into Giygas.
After all this time, the Nowhere Islands had drastically changed as well. Due to the forces of the world's plates, the islands split up even further, creating the geography that we know as the Pokémon world.
As in result of all these events, Pokémon now coexist with humans. However, this started never-ending conflicts between the two races, such as desires to rule the world, thoughts of liberation, and discrimination. Since the Dark Dragon had already split into three at this point, it could not end the conflicts and keep Lucas' wish. This also resulted in this legend being a lost legend that not very many know.