Step 1: Use all 1,000,000 stones in a slingshot to figure out it’s not tameable.
Step 2: Rage over that it’s not tameable
Step 3: Watch YT about admin commands
Step 4: Spawn one in using admin commands
Step 5: Forcetame it
Step 6: KILL EVERYTHING FOR NO REASON.
OK... you go to cerulean cave and go far throughout the maze and you find it... bring it's HP low and throw a ultra ball OR you throw ( waste) a master ball from the start of the match and... boom you caught yourself a MEWTWO! Good luck with the pokedex then...
Hehe- wait it's the overseer?! I thought it was mewtwo... well don't care about all what I said except if you wanna catch mewtwo but you dunno how...