you can't
you need action replay go to youtube to get the code
You dont catch mew You catch mewtwo in cerulean cave
You can't catch it at Pokemon Pearl, you'll have to Transfer it from LeafGreen/FireRed or trade it with SoulSilver/HeartGold
No, you cannot currently get Mew at Gamestop stores for Pokémon HeartGold or SoulSilver.
Nintendo event
Yes you can if you have Mew in your Pokemon SoulSilver/HeartGold You can put Mew in the Pokewalker.
No, Deoxys is only in Emerald, and you need to migrate it to can catch it. As for Celebi and Mew, you need a cheat code for them.
you cant for heartgold or soulsilver suckers
there is a mew in Pokemon soulsilver but you need to catch all leadndery Pokemon including event Pokemon
yes
An event
yes