You needed to get it from the 10th anniversary Mew event that went on in October 2010. If you didn't get it from that event then you need to cheat
To get a Mew in Pokemon Heartgold, you could do it through a Nintendo Wi-Fi event.
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
Mew can't be catched in Pokemon heartgold, only mewtwo.
you cant for heartgold or soulsilver suckers
you can't
Nintendo event
Mt.Moon