Depending on how much you weakend it, yes.
You may also need to put it to sleep or paralise or something!
------------UPDATE-------------
This was tested using an emulator and savestates:
It is 100% possible to catch Mew full hp using only a pokeball.
I believe I restarted the game close to 40 times before it went.
Hope this helps.
Get him down to 1 hp, confuse him, and then paralyze him. Then you might be able to catch him with a poke ball if you hack.
3 or 0.4% throwing a poke ball at full health it's better to use a master ball.
Master Ball
To catch a pokemon, you require a Poke ball, which you can buy from a poke mart.
a master ball or you can make it go to sleep and make it have low health and catch it with a ultra ball
masterball
Get him down to 1 hp, confuse him, and then paralyze him. Then you might be able to catch him with a poke ball if you hack.
3 or 0.4% throwing a poke ball at full health it's better to use a master ball.
Yes. It is completely possible to catch Mewtwo with an ultra ball.
You can catch Mewtwo easily by using a Master Ball on it or by using an Ultra Ball on it after lowering its HP.
I prefer to use my Master Ball for Mewtwo, but at least use an Ultra Ball.
MasterBall
you catch it with a poke ball
You can probaly catch him with a ultra ball but I would use the master ball
master ball
with a poke ball
use a poke ball