NO! don't cap mewtwo using the masterball!! here is what you do:
save b4 hand,
wekin him(paralize him is good in combination)
so by now you've done the basic pokemon cap'in steps now throw some fast ballls
throw more
THROW MORE
THROW MORE!!!!!!
then welcome mewtwo to your team >:-)
NOTE: you may run out of fastballs in that case go and reset(whell DUH)