Here are all the legendaries you can get without cheats: Groudon, Kyogre, Regice, Regirock, Registeel, Rayquaza, Latios/Latias.
no
Without cheating? You don't.
No, not without cheating.
a bunch
i think you have to trade them from other games
you carnt without cheating our hacking/codes
You can't...without cheating.
beat the battle frontier!
you can't
trade from other games
Mew is only available without cheating on Pokemon Emerald Version so you have to trade it from there.
It is rather unfortunate that you can not get Deoxys in Emerald, however, it is possible if you go to a Nintendo Event.