How do you get Mewtwo in Pokemon LeafGreen?

After you get the national Pokedex, go to the cave north on Cerulean City, go on the path you have to surf to.

Follow the cave's maze, and you should find Mewtwo at level 70! If you wasted your master ball then you will need to take about 60 ultra balls! in the cave you can catch a mewtwo. u need to go and roam around until u reach the centre. there u talk to mewtwo and battle it(save before fighting in cae u kill it).this catching of mewtwo helps but take notice that u catch it with a great or ultra ball. first i caught it with a great ball but then forgot to save it.so the next time i had to use my master ball cause i was bored and irritated. now my team is:

1.blastoise lv100

2.mewtwo lv100

3.zapdos lv100

4.tyranitar lv89

5.magmar lv88

6.snorlax lv96

save your masterball for the legendary dog

1.squirtle-raikou

2.bulbasaur-entei

3.charmander-suicune Mewtwo is in the cerulean cave. to get to him you need to:
1.beat the elite four
2.have a surf pokemon
3.have a rock smash pokemon

it's also good to have:
1. an escape rope/ dig pokemon
2. something to escape from shadow tag

Go into the cave, navigate the labyrinth, and save before you fight him.
Master balls will work but aren't necessary. I caught mine with a nest ball, and another one with a regular pokeball. Just make sure you bring plenty of whatever it is you want to catch it with.

good luck Follow these steps and you can have Mewtwo in about 15-30 minutes.

1. Defeat the Elite Four.

2. Get the Ruby and Sapphire.

To get the ruby, go on island 1 and go to the volcano. At the entrance, you will see some Team Rocket soldiers. Defeat all of them. Then go inside and go down to the bottom level. Pick up the Ruby.

To get the sapphire, go on island 6 and go to the Dotted Hole. Cut the door, and follow the directions for the braille icons. At the end, a super nerd will pick it up first, but he will give you the second password to the Rocket Warehouse (you already know the 1st one). Go on island 5 and defeat all the soldiers there. Go through the warehouse and at the end you will see the super nerd again. Defeat him, and you will get the sapphire.

3. Give the gems to the guy operating the machine at island 1 in the healing center.

4. Go to the cave in Cerulean City. Follow the maze (you will need Surf) and you will find Mewtwo. He is extremely hard to catch with an ultra ball, but you can catch with a master ball if you managed to save it. ask the question "How do you catch Mewtwo in Firered?"
Defeat the elite four and give the sapphire gem and ruby gem to celio. then go to the cerulean cave and its in there as a level 70. Tip try to get it with an ultra ball. Get entei, raikou or suicune with master ball. if you do not have an action replay, you go to Cerulean Cave after fixing Celio's time machine and go through the maze. At the end is Mewtwo.

LAT MAN RULES (DOWN) (TO CATCH HIM)

the best way is to get Pokemon that know moves like paralize and sleep but not burn or posin (that might kill him) buy alot of ultra balls and get false swipe and state reducers mewtwo is level 70 so hes tough. get high leveled Pokemon too.(snorlax is a good choice just don't delet any moves it knows when caught)

LAT MAN RULES(^)