You have to help the CopyCat girl in the Pink House in Saffron City with her problem (after you defeat Red). After completing her task, she'll give you the train pass. You can then go on the magnet train.
soulsilver and heartgold, it has the most trainers
train them a lot to around 20
train your pokemon up to level 80,90, or 100 and teach it TMs and HMs
you have to train or talk to them. well only you can talk in soulsilver or heartgold. i have played .
Train
train it
train it
You must "endlessly" train your Pokemon.
the elite 4
To see a Pokémon's happiness in HeartGold or SoulSilver, you take them to Goldenrod City, where there is a house where you can check your Pokémon's happiness there. It is on player's right-hand side, and is in the little section right below the Magnet Train.
You cant. you have to train.
Train mareep