Rayquaza, Groudon, Kyogre, Regirock, Registeel, Regice, Latios/Latias, Mew (event only), Deoxys (event only), Lugia and Ho-oh (also event only).
-And Jirachi-
In emerald without a mystery gift or anything, you can catch Groudon, Kyogre, Rayquaza, Regice, Registeel, and Regirock.
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