keep on soft resetting your game until it is shiny or cheat
well, you catch the regular rayquaza at sky pillar.this is near pacifilog town. if you want a black (shiny) rayquaza, save before you battle it, and keep turning off the game until one is shiny! he is very hard to get.
you know how to catch a rayquaza at sky pillar then you have to try atleast 8,192 times because the chance of getting a shiny is 1 out of 8,192
You cannot catch rayquaza in fire red you must trade from either ruby or sapphire.
You Can Only get A Black One if It's Shiny. Other Than That You Can't And There Is A VERY thin chance of getting one.
master ball
Sky Pillar
save and repat versing until you get him
any Pokemon can be caught shiny from the second generation onward, so you could catch a shiny rayquaza in emerald/Sapphire/ruby all you need to do is play through the game enough times to find it. some get lucky with the first few 1000's but shiny chance is 1 in about 8120 i cant remember exact number but 8126 feels right
you have to transfer it from emerald,ruby,or saphire.
you cant catch rayquaza you must trade it from emerald
you can catch groudon in ruby in cave of origin then beat the elite four to catch rayquaza on sky pillar
Trade from emerald/ruby/sapphire.