I don't think you can battle Gardenia in Pokemon HeartGold.
No, but you can trade Pokemon only in HeartGold to Black
you can trade pokemon from heartgold to black but you can only transfer the pokemon in heartgold not trade it from black
let your Pokemon battle
No, you can't battle Maylene and/or Crasher Wake in Heartgold.
I don't think you can battle Gardenia in Pokemon HeartGold.
He does not appear in Pokemon Black or White. He only appears in Gold, Silver, Crystal, HeartGold and Soulsilver if you want to battle him.
No, but you can trade Pokemon only in HeartGold to Black
in Pokemon white, black, platinum, heartgold, soulsilver, diamond, and pearl you do not need to battle anybody
you can trade pokemon from heartgold to black but you can only transfer the pokemon in heartgold not trade it from black
let your Pokemon battle
After Diamond and Pearl, there's Pokemon Platinum, HeartGold and SoulSilver, Battle Revolution, My Pokemon Ranch and then Pokemon Black and White.
No, you can't battle Maylene and/or Crasher Wake in Heartgold.
you can transfer it from Pokemon soulsilver/heartgold to Pokemon black
Ash is not in Pokemon HeartGold, but Red is able to battle on the Summit of Mt. Silver.
No you can't
you dont.