In emerald only here's all the Pokemon you can get: Mew (event only) Latios and Latias, Groudon, Kyogre, Rayquaza, Deoxys (event only) and lugia and ho-oh (event or get one from Pokemon colosseum and Pokemon xd gale of darkness), also if you trade the legendary birds from leafgreen and firered to emerald you can have them and you can have mewtwo also celebi (event only) and jirachi (Pokemon colosseum pre ordered special disc) also the legendary dogs raikou, suicune, entei from firered and leafgreen and last but not least the regis regirock regice and registeel.
Kyogre,Groudon,Rayquaza,Regirock,Regice,Reggisteel and either Latias(red on t.v.) or latios (blue on t.v.).
all the legendaries and how to get them here http://www.psypokes.com/emerald/legendaries.php
its not an emerald its RAYQUAZA the main legendary Pokemon in Pokemon emerald.
Use Gameshark.
beat the Pokemon league in fire fed and emerald then trade them and if you want duplacat them.(duplacating only in emerald)
You have to trade it from FireRed or LeafGreen
all i know is how to get the regis and latios or latias.
rayquaza
The three legendary Pokemon in Pokemon emerald is Kyorge, Groundon and Rayquazer.
Groudon, Kyogre, and Rayquaza. Groudon is the fire legendary pokemon, Kyogre is the water legendary pokemon, and Rayquaza is the air legendary pokemon.
Raquaza (sorry if I mispeled that)
There are no breedable legendary Pokemon in Emerald. In Diamond/Pearl/Platinum Manaphy is breedable with a Ditto. However, the offspring will be a Phione.
No,but you can migrate your legends from firered leafgreen emerald ruby or sapphire