A masterball would be the best choice but if you want to save it, you should use a Pokemon that does not let him flee (he always flees after the first turn) and use regular pokeballs or ultra balls
Chat with our AI personalities
you can put it to sleep/paralyze it etc. than use 100+ ultra balls
Just be paitent and catch it with a pokeball!
MasterBall
Any pokeball will work but an ultra ball is probably best.
A Master Ball