You catch them all....
Pokemon HeartGold can communicate with all the DS Pokemon games. :c)
I put a link to a guide all about legendary pokemon in HeartGold in the related links.
no
you get all the Pokemon
Nope problaly not!
Yes.
There is no best Pokemon on Pokemon HeartGold.
No, you can't get all of the Legendaries in Pokémon HeartGold although you could trade all of the Legendaries in.
there is no Pokemon Mansion in Heartgold.
you throw pokeballs at them
migrate and trade
yes u can in all pokemon games