You can't catch a Forretress in Heartgold or Soulsilver though you can level up a Pineco of which you can find one in New Bark Town and you use headbutt on the trees there.
They are not in Pokemon HeartGold
You cannot get Dialga in HeartGold version.
you can't get sinnoh in heartgold.
Hoenn is not in heartgold version, only johto and kanto are in heartgold, hoenn is in emerald
HeartGold is the correct title.
Shadow Lugia is not in HeartGold.
You have to trade it to HeartGold from P/D/Pt
In heartgold please :)
There is no TM transform in Pokemon HeartGold
you can catch lugia in whil islands in heartgold
Only by trading a Squirtle to HeartGold.
there is no Pokemon Mansion in Heartgold.