After defeating the Elite Four, get to the Weather Institute on the second floor and talk to the Weather Professor. He will tell you that there is a heavy rainfall at a certain route. Got to the route told by him and there must be a place to dive that wasn't before. Dive and get in the cave and there must be Kyogre.
You can't get Kyogre in Pokemon Ruby but you can get Kyogre in Pokemon emerald and sapphire and in ruby you only get groudon and rayquaza. In sapphire you get Kyogre and rayquaza and in emerald you can get groudon, Kyogre, and Rayquaza.
In Pokemon Emerald, Groundon and Kyogre are legendary Pokemon. You can find them in the Marine Cave and the Terra Cave.
The best water Pokemon in Pokemon emerald I believe is Kyogre. kyogre is probably the stongest but i prefer a swampert if you don't like legenderies
Kyogre is available in Emerald and Sapphire but not in Ruby.
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KYOGRE!
Kyogre.
There is no cheat to obtain Kyogre in Pokemon Ruby. To obtain Kyogre and Pokemon Ruby, one must trade with a trainer that has obtained Kyogre in Pokemon Sapphire or Emerald.
I do not know if you can catch Kyogre in Emerald but if you could, Kyogre will be in the Cave of Orgin at Sootopolis City. ;) ANSWER At marine cave, but I dont know how to get there
not much only in sapphire you can only catch kyogre and in emerald you can catch both kyogre and groudon.
Kyogre.
You must trade kyogre from sapphire or emerald to firered to obtain it.