First u need to beat the elite four then get(catch) 60 pokemon and talk to prof oak and he
will give u and ur rival a national dex then go to isle 1 and talk to celio after talking
to him he will ask u to get a ruby and go to mt ember far then walk and surf after the spa
til the mountain and find the two team rocket guys that are bloking ur way defeat them and
retreive the ruby and bring it to celio step two celio will ask  u to go to get him a
shaphire now and he will give u the rainbow pas to acsses isle 1-7 then go to island 4 or
5 not shure and help loreilli of the elite four in the ice cave then go to isle six and
get to the steel door get infront of it and use cut and go in and retreive the ruby inside
u go up there is holes first u go in the top one then the left then right then bottom or
if that doesent work try the top one then right one then left one then when u are abount
to take the shaphire there is a scientist that will take it from u and u have to go to
isle4 or 5 and go in the rocket whaare house and get it for celio then give it to him and
now u can get mewtwo in the curlean city cave hope it helped urs truly ilovecelebi