The best place to get exp fast is cerulean cave where you find Mewtwo. Hope i helped.
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in heart gold cerulean cave in platinum i don't know
Train it.
Mt. Silver,Mt.Silver cave and victory road.
Goldenrod City
an easy way is to trade a bunch of your good Pokemon onto Pokemon heart gold but if you don't have a lot of good Pokemon on heart gold and you don't have another game then train a lot before you get there :)
The best place to evolve a Pokemon in Pokemon Heart Gold is at Mt. Silver.
elite 4 or mt silver
It is next to the train station in a little crook of the town.
It's Darkrai. You can't get him in Heart Gold.
Pokemon Heart gold is different from Pokemon Gold cuz heart gold has better graphics new Pokemon and new events
The best place I know is victory road