For a step by step made clear please see related link.
Or if you already used the masterball on a different Pokemon, you can buy lot of timerballs from the pokecenter and keep very strong Pokemon with you (about levels 80 or higher.) once you are battling Mewtwo, keep battleing until you battled him for quite a while. Then! use a regular pokeball, then an ultraball, then timerballs until you catch him. That is what i did and i obtained him. ^_^
Edited by Jolene_Lacey66
Answer
to get mewtwo, u must have done the following:
1. Beat the elite 4
2. get the national dex from professor oak (must have caught 60 Pokemon in order to get it)
(then u get the ruby and sapphire for celio)
How to get....
Ruby: to get the ruby, u have to get the national dex first then go to celio on 1 island. talk to him and he'll ask u to
get a ruby for him. the ruby is in mt. ember where moltres is. when u get to the top (not where moltres is) go to the
right and u will see 2 rocket grunts. battle them and go inside the cave. once u get in u just have to go find it.
look on YouTube if u can't find it. (u will need a Pokemon who knows strength)
Sapphire: to get the sapphire, u will need to go to the dotted hole on 6 island and use cut on the door. once u get inside,
follow the following directions:
up
left
right
down
and u will end up at the gem. when u get closer to it, a scientist will come and steal it from u.
now u will have to go to the rocket warehouse on 5 island. u will have to get through the maze and find the scientist who
stole the sapphire. when u beat him, he will give u the sapphire. then go back to 1 island and give the sapphire to celio.
Mewtwo:
Go back to Cerulean City and go up onto the nugget bridge and surf down to Cerulean Cave and find mewtwo.
Hope I helped :)
Edited by: Devin_son
Here is some more additional info:
I tried to play Pokemon Leaf Green , the 4th time now. And i usually catch Mewtwo with a Master Ball. But yesterday i got some luck and i got him this way:
1. Go to Cerulean Cave after you did the tasks for Celio is the Sevii Islands.
2. You will need the HMs Surf , Rock Smash.
3. Take with you some Max Repels ( If you wanna do it quick ) or just battle the cave's pokemon which are around levels 49-66 i think - for some exp.
(Wobbuffet,Golbat,Kadabra,Machoke,Magneton,Parasect,Ditto, Electrode)
4. Dont forget your pokeballs. I had used 6 Ultra balls and 1 Luxury ball to catch Mewtwo ( Cool , isnt it ? )
5. Patience and Luck ! :)
Hope i helped - Ms Trix.
Once you beat the elite four for the first time, you have to go on the Sevii Islands. After you met your rival there when he said that he will go back to the continent. Go beat the elite four a second time and then, go to the Cerulean cave. Mewtwo is inside
first beat the Pokemon league then catch 70 Pokemon then go to cerulean cave go inside and go find mewtwo. good luck
just beat the elite four fix the network machine on island 1 and u will unlock cerulean cave in cerulean city. go across nugget bridge. there will be grass with a strip of water surf following the water and go in cave. let the game lead u from there, its easy to find. buy 58 ultra balls or ur masterball if havent already used it. i cught him with starting 58 ultra balls, remaining 14.
Mewtwo, yes, if you have a FireRed or LeafGreen with Mewtwo.
Capture Entei/Raikou/Suicune.
Nope, you have to trade him.
go to the special event
You can't catch it on Firered you can only catch it in Emerald
Mewtwo, yes, if you have a FireRed or LeafGreen with Mewtwo.
You can't get mew in firered or leafgreen.
sadly,no
The Cerulean Cave
There no Mew in firered.
You must capture Mew on Emerald and trade it to FireRed.
Mew two sould be at the end of the cave in cerulean city after you beat the elite 4.
Capture Entei/Raikou/Suicune.
how did u get mew
You cannot get Mew legit in Pokemon FireRed, for the event for Mew has ended. You would need to use a GameShark or trade for it from Pokemon Emerald.
mew
no