you must trade it to platinum pearl or diamond and level it up by the moss rock. as long as you trade it back to the original trainer afterwords, it wont act like a traded pokemon, so make sure your eevee is from your heartgold game.
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To get both leafeon and glaceon in Pokemon soul silver or heart gold you have to trade it from diamond pearl or platinum.
To evolve your Evee into Leafeon, get a leaf stone, and use it on Evee, and it will evolve into Leafeon! Have fun with Leafeon! -Garrett
To get a Shedinja in Pokemon Heart Gold you must trade it from either Pokemon Ruby, Sapphire or Emerald. Jacko25
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you don't get the red orb in Pokemon heart gold you get the blue orb that you use to get kyogre