I can see them all
The ones who started it
The rumor that I am not who I am
That I am someone else, an unintended mistake
But they are darkened, many times over
As I flit about from here to there
In rainy weather, on windy days
In search of ancient medicine
I have three stretched guesses.
Porygon/Porygon2/Porygon Z
I can see them all - Porygon can travel through a world called cyberspace and see everyone through technology
The ones who started it. The rumor that I am not who I am. That I am someone else, an unintended mistake - In Porygon's first and only major appearance, the episode was banned due to seizures and with that, Porygon with people jumping to the conclusion that it was Porygon's fault. In actuality, it was Pikachu who caused the beaming lights.
But they are darkened, many times over - It's thought that Porygon is one of the few Pokemon that might be capable of flying through actual space.
As I flit about from here to there - Porygon can travel places in an instant through cyber space. Porygon-Z can travel places in an instant through worm holes.
In rainy weather, on windy days - Porygon can blend in it's surroundings.
In search of ancient medicine - No clue.
Celebi
I can see them all - Celebi is capable of time-travel.
The ones who started it. The rumor that I am not who I am. That I am someone else, an unintended mistake. - A stretch but perhaps it has to do with the GS Ball, an episode that was supposed to feature Celebi but was shelved for the movie.
But they are darkened, many times over - Not a lot of people realize that GS Ball contains Celebi, an event that only appeared in Japan previously.
As I flit about from here to there. In rainy weather, on windy days. - Celebi can move along the passages of time, past many people.
In search of ancient medicine - There's a legend about Celebi in the Pokemon Adventures manga where it rewarded a person with ancient medicine.
Entei
I can see them all - Entei can reach to any location in a matter of seconds
The ones who started it. The rumor that I am not who I am. That I am someone else, an unintended mistake. - Entei is described as the fiercest of the three legendary beasts, Pokemon reborn from three unknown Pokemon by Ho-Oh and Pokemon that people feared long ago due to it's resurrection seen as unnatural.
But they are darkened, many times over - Entei constantly escapes from many powerful trainer's grasps
As I flit about from here to there. In rainy weather, on windy days. - Entei is known to be extremely fast as seen in his move, extreme speed.
In search of ancient medicine - Sacred Fire has healing properties and is a move passed on by Ho-Oh