To evolve Porygon when it holds the item 'upgrade' and it is traded over to another game. It will evolve into Porygon2.
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eiquip it to porgon then trade it to get a porgon 2
you have to beat the trainers and the time in that place on seven island
Yes you can trade leafgreen version Pokemon to another leafgreen version.
get the upgrade in the rocket warehouse on Five Island and then trade to another GBA game and then it will evolve. (porygon can be bought at lv. 18 at celadon game corner, and must be holding upgrade to evolve.)
On Pokemon Pearl's title screen, if the Pokemon LeafGreen game is in the GBA slot, click on "Transfer From LeafGreen" and you can choose six Pokemon from LeafGreen to transfer to Pearl, but be careful-you can't trade them back.