It took me a while to figure this out but im happy to share this. First go to dotted hole,and use cut. then fall in the hole. There's more holes, so fall in this order, up,left,right, and down. Getting the saphire will bring some dimwit into the cave with you. he'll take the saphire, yet give you the rocket warehouse password. What a dimwit. He'll leave, so follow him. get through the ware house and beat the rocket admin. then she'll let you go in and out from there freely. beat the other adnim and they will disapear. Then the ceruelan cave kid will let you inside. Get through the cave and catch mewtwo. only works after the elite four.