you cant unless you migrate
Every Pokemon from every region except Unova
Do you have every Pokemon in the game? If not, NO!
almost in every city in Pokemon
yes you can catch every Pokemon ever made
in every Pokemon centre and some other places as well
yes because in Pokemon HeartGold and SoulSilver you travel to every region.
You can find it in any Pokemon Center and that's for every single Pokemon game (That I have)
There is no best Pokemon on Pokemon HeartGold.
There is a Pokemon center in every mapped town in every Pokemon game except for the Rangers and Explorers.
No it does not have every Pokemon you can get more types of Pokemon by trading at the GTS or without wi-fi at the second floor of the Pokemon center with the middle lady. hope this helps ;)
there is no Pokemon Mansion in Heartgold.
They are not in Pokemon HeartGold