It evolves porygon to porygon2
you trade it while holding an up-grade.
King's rock, Dragon Scale, Up Grade, Metal coat.
You can get in the rocket hideout Which is in the five isle meadow. You can also get it when participating at the trainers tower. (do single mode battle.)
To evolve Porygon when it holds the item 'upgrade' and it is traded over to another game. It will evolve into Porygon2.
you train them!!!
Level them up.
Yes you can trade leafgreen version Pokemon to another leafgreen version.
up your bum
If you trade Pokemon between leafgreen and ruby ruby will have your leafgreen Pokemon and leafgreen will have the ruby Pokemon both in the party they will not be sent to the PC unless you personally walk to the PC and do so.
beat a trainer and search the Pokemon up in your Pokedex
Not in Pokemon leafgreen only in Pokemon Firered never ever in Pokemon leafgreen And in Pokemon firered it is rare in power plant not available in Pokemon leafgreen?
you can only find it :-(