I think it's just Rayquaza, not sure where though.
There are many Pokemon you catch that are similar in sapphire and emerald but there are many Pokemon emerald can only get and not sapphire.
I don't now but I believe that you can catch as many as you want when you encounter them.
All if you have a gameshark
there are three that you can CATCH in pokemon emerald its Groudon, Kyogre, and rayquaza regice registeal regirock litos lotias
In the Pokemon center you can hold either 430 or 450 i forget. and you team.
you have an awesome team but you're using too many legendaries take latios out and put in a electrical Pokemon or a dark Pokemon because you have 3 Pokemon that are legendaries.
In general, there are 6 legendary Pokemons in Emerald. If you count the Event Pokemons in Emerald, then there are 12 legendary Pokemons in Emerald.
51
there are many legendaries to catch in pearl palkia - spear pillar cresseslia - new moon island heatran - stark mountain rotom - old chateau regigigas - snowpoint temple plus many more :)
There there are 36 legendaries all through out the Pokemon regions but there are Arcanine,Gyarados,Milotic,Rotom,Unown,Dragonite,Tyranitar,Selemence,Metagross,Garchomp, Ninetails,Lucario,Togepi,Absol and Spiritomb which i consider legendaries so that makes it 51 if you believe they are legendaries and they will also make more legendaries in the future of Pokemon hope i helped also i have all the legendaries and wouldn't mind trading them to Pokemon trainers or collectors. Contact me at trippyranga@hotmail.com
for me emerald because you can catch all Pokemon and you can find many shiny Pokemon i think emerald bec you can get almost all pokemon on it bec you can get the moon thing or susket but other than that ya emerald when you do get rayquaza kyogur and groundon they are lvl 70 all of them in pokemon sappire you oly get a lvl 45 kyogur (sorry for spelling)
you win the game! but, you can always go back a fight him again, and do many other things like: complete pokedex catch legendaries train Pokemon