SPOILERS, NOT RECOMMENDED TO READ UNLESS YOU HAVE GOT THIS FAR.
Elite 4 Sidney
Mightyena: lvl 46 ability: intimidate
Cacturne: lvl 46 ability:sand veil
Shiftry: lvl 48 ability chlrophyll
Crawduant: lvl 48 ability shell armor
Absol: lvl 49 ability pressure
weakness: fighting types will kill them all
Elite 4 Phobe
Dusclops lvl 48: ability pressure (note, Dusclop's first attack wil ALWAYS be protect)
Dusclops lvl 51
2x Banettes at lvl 49
Sableye lvl 50
weakness: Hi dark type
Elite 4 Glacia
2 Sealeos and Glalies 1 at 50 1 at 52
Walrein lvl 53
weakness: fighting again
Elite four Drake
Shelgon lvl 52
Altaria lvl 54
Kingdra lvl 53
Flygon lvl 53
Salamence lvl 55
Weakness... Ice type, only Kingdra is not super effective to it, but Dragon types are a nice substitute if you don't have Ice Beam
Champion Wallace
Wailord lvl 57
Ludicolo lvl 56
Whiscash lvl 56
Tentacruel lvl 55
Gyrados lvl 56
Milotic lvl 58
weakness: I think I'll go into a little detail.
For Wailord,Tentacruel,Gyrados, and Milotic, use Electric. Ludicolo is incredibly annoying if he pulls off even 1 successful attack, use flying or poison, if you have Swalot and ability is liquid ooze, Ludicolo's best attack on it is surf. Whiscash, a nice high level Tropius clost to or above 50 wil prove very effective on it. A full team is recomended. If you think you can catch him, go back to Sky pillar and catch Rayquaza. He's at lvl 70. You need the Mach bike to get to him. He's not that hard to catch. Good luck