It can be as few as a single one or as many as dozens of them. It all depends on how the game's RNG for capturing Pokemon decides to treat you.
about 20
well for me it took me 20+ ultra balls. It all depends on how lucky you get.
You need 21 ultra balls to catch Heatran
for me what i did i didnt have any ultra balls all i had was 10 great balls and i used mega kick with my blastiose and used about 5 great balls and caught it :^) -drew
There are many types of PokeBalls you could use to catch Azelf.But I would suggest the following: Quick Balls Master Balls Poke Balls Dusk Balls and,Ultra Balls
i caught it first time in a great ball
depends on how weak he is and how lucky you are
it takes at least thirty i caught mine with a ultra ball but before i did that i lowered its health to almost red at the end of yellow use a few dusk balls and great balls before using ultra balls
Weaken it to red hp, paralyze it then use many net balls or ultra balls.
Do you mean articuno then simply use many ultra balls after weakening it.
first buy as many ultra balls you can and battle Mewtwo. Once his hp is low start using the ultra balls (just keep trying until you got him)
learn the braille alphabet and do what the writing on the wall in regices cave says. take many great balls, ultra balls, and timer balls