Before I go on, I'd like to say that without a Cheating Device, you cannot get these Pokemon from HeartGold.
Deoxys - Migrate from the GameBoy Pokemon Cartridges to Pokemon Pearl or Diamond by using the Pal Park. Afterwards, trade Deoxys to HeartGold or SoulSilver. (By the way, Deoxys can be found at Birth Island in the GameBoy Pokemon Cartridges.)
Mew - It seems that Emerald is the only GameBoy Pokemon Cartridge that has Mew. Migrate Mew to Pokemon Pearl or Diamond, like Deoxys, and trade it to HeartGold or SoulSilver. (Mew can be found at Faraway Island in Emerald.)
Celebi - Migrate from the GameBoy Pokemon Cartridges to Pokemon Pearl or Diamond by the Pal Park. Do the same with the others and trade Celebi to HeartGold or SoulSilver. (Nintendo Event is needed for this lovely Legendary.)
Celebi
you find out in the celebi event, but it deals with Giovanni.
To get celebi, there is an event that has only been realeased in japan
this is it: 52247d8c 582000c0 12247d8a 00004801 02247d8c e0021c39 02247d90 000000fb d2000000 00000000
you use it to put in the shrine to cath celebi
There are only a few you can catch but the rest you have to get from trades with other games.
The only way to get a Deoxys in Pokemon Heart Gold is to either trade it from another Pokemon game that has it, or use an action replay code.
Guys get this.....It's the same thing with deoxys through Pal park
Celebi
It's the pokemon, Celebi.
It is an event
Jirachi, Groudon, Regiice, Regirock, Registeel, Regiggigas, Arceus, Mew, Celebi, Deoxys, Latios, Shaymin, Darkrai, Cresselia, Manaphy, Phione, Rotom ,Azelf Uxie, Mesprit,Giratina.
Deoxys is only available for capture in the 3rd gen games, so you have to transfer it over.
Up ur pe nis
You need a fateful encounter one
well you cant catch it in Pokemon white you have to get it in Pokemon heart gold or soul silver using an event IF YOU ONLY WANT CELEBI WELL YOU CAN ALSO GET ZORUA IN CASTELIA CITY WITH CELEBI SO ID DO THAT ONCE YOU GET CELEBI
you cant, you must get it from a trade or cheating,hacking,or glitching