A good way to beat Mewtwo (Lvl 70 in Soul Silver, assuming you don't want to catch it) is by using your Starter Pokemon (Should be full evolved, high level) and Pokemon with Endevour might be a big help. BEWARE THAT YOU DON'T GET MUCH EXP. FOR THIS.
If you want to catch Mewtwo, i would suggest training up a Parasect (Learns Spore and False Swipe) to lower Mewtwo's health, also train up a Sceptile or another Pokemon that can learn False Swipe, so if Parasect faints, another one can take over.
Lvl. 70
Strong.
I recommend using Timer, Ultra Balls on it.
First you have to beat all of the Kanto gyms. After that you go to the Cerulean Cave. At the end of the cave you find Mewtwo.
Mewtwo is inside the Cerulean Cave in Cerulean City. You have to beat the entire game in order to go inside and catch it
If you want to catch Mewtwo in Soulsilver , first , beat the elite four, then get all 8 badges in the Kanto region, then you beat red at the top of Mt. silver, after that fly to Cerulean city in kanto, go to route 24 and surf to the cave in cerulean. Deep in that cave is where you find mewtwo!
Beat the game first, then go to the Kanto Region, and then there is a cave in the city where a guy was blocking it earlier, but now since you beat the game you can go into the cave and find Mewtwo.
deep in cerulean cave but you have to beat all the kanto gyms before you can go in
Get all gym badges Beat elite four 1 time he is in cereleun cave
After beating the 16th Gym leader, you can Catch Mewtwo, and then just train for Red.
mewtwo is in kanto it is in cerulean cave
Yes, Mewtwo, Latios and Latias will be in HeartGold and SoulSilver.
If you mean how to consider yourself as beaten the kanto region in pokemon soulsilver, then you should find zapdos,moltres, and articuno. You should also beat Red (Ash Ketchum). Once you do that, you can catch Mewtwo.
you find it in the cerulean cave behind cerulean city after you beat all the Kanto gym leaders
Cerulean Cave.