You have to go to Saffron City in Kanto (the city with the Poison type Gym) and speak to Copycat, who lives in a small pink house two alleyways up from the Pokemon Centre. Speak to her in her room and she will do a copy of you, telling you that she lost her Clefairy PokeDoll and she lost it in Vermillion City. Go to Vermillion City and go to the Pokemon Fan Club. Speak to the man sitting at the table (the one with the Clefairy statue and now the Clefairy PokeDoll). You tell him about Copycat and he is upset that he made her sad. You obtain the PokeDoll and now you have to Fly back to Saffron City. Go and talk to Copycat. She will thank you and you will be rewarded with the Magnet Train Pass.
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after you get the magnet train pass use the magnet train
get clafairy doll for copycat girl in saffron
go to magnet train manger and ask him to give you a train pass
you can ride the magnet train
You can use it to take the magnet train to kanto I think.
you go to the Pokemon tower
You can now use the train from kanto to johto.
you have to find copycats clefairy doll give it to her and she will give you a magnet train pass hoped it helped you out kieran Thompson
You need to have mewtwo to get it
You talk to the copycat girl in the city with the magnet train in Johto and bring her her pokedoll from viridian in Kanto
Get on the magnet train and it will take you to Goldenrod city. You can back and forth between johto and kanto easily using the magnet train, but it's not essential.