you can't
Certai pokemons that come from events are not needed to complete the pokedex. Such as: Arceus Mew Deoxis Manaphy etc...
you have to trade them over
To get a Mew in Pokemon Heartgold, you could do it through a Nintendo Wi-Fi event.
Mew is #151 in the national pokedex, and it is a Psychic type Pokemon.
Yes you can if you have Mew in your Pokemon SoulSilver/HeartGold You can put Mew in the Pokewalker.
yes
An event
yes
Mew
mew
Pat yoursef on the back and move on to the next game, or complete the pokedex.
You must catch every Pokemon 1-493 except for Mew, Lugia, Ho-oh, mewtwo, and Deoxys.