You can exchange them with the Move Tutor in Fallarbor Town. He can teach your Pokemon a move that it learnt in the past but doesn't know anymore. This is useful if you accidentaly delete your best move, etc.
Chat with our AI personalities
Catch a bunch of luvdisc they can hold heart scale.
Heart scales are only in Pokemon emerald, ruby and sapphire but you can get one if you trade a heart scale from ruby or emerald or sapphire to leafgreen then take it but it will not do anything in the game.
you cant get one on leafgreen you have to trade it over from ruby Sapphire or emerald
u go to the move deleter at fallorbar town.you need a heart scale.
You can't migrate from HeartGold to Ruby. But it can be the opposite. Pokemon can be migrated from Pokemon Ruby to Pokemon HeartGold.