Guys, I performed a long-range glitch with a team rocket grunt in mt moon and I battled a youngster in mt moon and when done I go downstairs in mt moon and the game automatically pressed start and when I closed the menu and I found a exeggcute
You performed what is closed the mew glitch. Using this glitch you are able glitch spawn all the Pokémon in the kanto region and even a few trainers. Plus you can glitch spawn missing no. I will edit this answer later if you want more info, but currently this answer meets the standards of you question. Actually I will answer how to do glitch.
Ok so to get whatever Pokemon you want, you will need the Pokemon with the special stat equivalent to what number it is next to in the second link. I have no idea how to explain this, but hopefully this helps.