Kyogre is a water type, and being pure water, it's only weakness is to electric and grass types. Using calm mind to boost sp.def, Kyogre pretty much lose all weaknesses. With an insane sp.att and sp.def, Kyogre reaches the point of near immortality except to Blocklax (who is completely invulnerable after full curses... currently i can't think of any counters to a Blocklax after it is fully cursed)
However Kyogre got somewhat weaker now as it lost ice beam for ancientpower, as Shedinja did earn the nickname of "Kyogre Mauler" awhile ago. This got the Kyogres so paranoid that they dropped ice beam for ancientpower to kill off the Kyogre Mauler. So now it probably got surf and ancientpower as its attack, and so now any Pokemon with Water Absorb can pretty much make a draw with Kyogre wasting all of Kyogre's precious PP, or force the trainer to switch (pseudohaze).
Kyogre is pretty hard to beat even if you're using Lanturn with thunder, or another electric Pokemon. Even Zapdos will have a very hard time with it after a few calm minds.