You can train in Victory Road, Match Call from your Pokenav, or fly over to Petalburg and Surf all the way to Slateport, beating every trainer on the way there. There is also a nice little spot to train on the left side of Pacifidlog town.
personnaly, my tactic consist in capturing rayquaza just befor doing it than fly there and buy many revive and potion.
then u just rush in with ur rayquasa and you heal him beteen each elite four.
another trick i use, is a sacrifice : if he dies, revive him with another pokemon that will than most of time die(i dont know for u but me it is most of the time some crap pokemon i didn't train XD) and get back ur raqyquasa.
if u dont have revive, change pokemon, he will get hit and if he die ur next pokemon can use a potion
i also sujest u try not to waste ur masterball on rayquasa if u want to duplicate it later in batle frontier. just save in front of him and keep using all ur balls until u get lucky and catch it
it can be an idea, but all i used was swampert lvl 60, rayquasa lvl 70(when i started leage, he may have got more when i arrive to wallace) and 4 creepy pokemon just to revive. it was hard against wallace and his kingdra i thinck that have rest? and ice wich is super effective agains rayquasa but i got him 1 time using my swampert, he could suvive more than 1 attack so when i change for it i could revive many creepy pokemon and than revive rayquasa many time :P
i thinck the sollution is all in using well his attack and having many items to restore ur pokemon, i thinck i had 20 hyper potion 30 full restor, 20 full heal, 20 or 30 revive and the most important of all (use befor wallace...)...elexirs or 1 max elexir. (i sujest u keep at least 1 max elexir for duplication after e4 ;) )
Guess what guys? The fact that he has Charizard, Blastoise and Venusaur means that he's either hacked or is playing R/S. If it is the former, he (clearly) can help himself. Otherwise, Rayquaza isn't available, and thus Victory Road grinding is his only real option.
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