You can't.
You are always in Sinnoh.
there is no possible way of catching piplup chimpchar or turtwig in heartgold or soul silver, you would have to trade it wirelessly or by wifi from pearl diamond or plantinum. Hope i helped enjoy the world of Pokemon peeps. Not to make you sad but its spelt Sinnoh xx
Rowan gave you a pokedex for a reason
For Shinnoh:493 Isshu:649
The next series is called pokemon black and white
You have to see all the Pokemon in Shinnoh. (You do not have to beat the Elite 4)
transfer the Pokemon from gba game into pal park and capture
no, not necessarily, you do however need the nationalDex which you get for seeing all 150 Pokemon in shinnoh
There is no best Pokemon on Pokemon HeartGold.
there is no Pokemon Mansion in Heartgold.
find em all stupid
They are not in Pokemon HeartGold