I know how to get Mewtow. In order to get Mewtow, you first must know where Cerulean City is. If you know, then you might have noticed about the walls surrounding all that water. If you look far enough, you will be able to see a guard gaurding some kind of tunnel. That tunnel is where Mewtwo is. In order to get the guard to stop guarding the cave, you must beat the pokemon league meaning you have to beat all the gym leaders in order to get through it, then you will have to get through Victory Road which leads to Indigo Platuea, then you have to battle the Elite four which are the hardest trainers in the whole game. After that, you will meet Gary, somewhere then battle, then I think, you will have to do a few more things. Once your are done with that, you will have to fly to Cerulean City and see that the guard will not be guarding the cave anymore. In order to get to the cave, you must have a pokemon that does surfing like Lapras. Then, you go through Nugget Road, then you make a left, if you make another left all the way to the end until you hit the wall, make another left, then you will be in a grassy area. Go all the way down. You might have to battle a few trainers. Then after that, you will come to a water area. At that moment, get your pokemon that can surf than let it surt on water. You'll be able to find your way to the land before the tunnel. Once you get on the land, just go into the tunnel. You will just have to work your way through the tunnel until you find Mewtow