mewtwo

Yes it is possible. It will most probably take you ages, so stock up on them before you try battling him. Don't tell me you used your masterball on a legendary bird?

Try getting Mewtwo down to minimal health and put it to sleep.

It is possible because I caught mine with ultra balls but it took 1 hour

Well I caught mine with a great ball so I say do this get a pigiot and teach it feather dance then use a laprs to use ice beam until it fresses then use a great/ ultra ball

Of course it's possible. Any thing is Possible! ~_^ All you need to do is weaken it to the point that it's red. Then try Paralyzing it, and putting it to sleep. Confuse it if you get the chance. Then start throwing Ultra's at it.

Yes it is possible but to get it you have to stock up save money until you have enough for 100 ultra balls or something around that and weaken it but DO NOT poison/confuse/burn it because it may get KOd if it attacks while confused and poison/burn will slowly kill it so put it to sleep,parlyze it,or freeze it.Then THROW MAN THROW!
I hope this helps!
-MUDKIPTORCHIC
P.S.You can do this with any Legendary Pokemon
P.S.S.Save BEFORE confronting the Legendary Pokemon
P.S.S.S.Bring like a level 20 Pokemon with you so you can use that pokemons attacks to bring it's HP down without KOing it

Yes it is possible I catched Mewtwo with an ultra ball it did not take long to catch it as well just get it to 1hp or low hp and it should work if you want to get it to 1hp you will need a strong Pokemon that knows false swipe