Verified answer

Try using Dusk Balls, they have a good catch rate when used at night and in caves, which is good since Zygarde and Mewtwo are both found in caves.

Maybe you ought to use the Master ball on a shiny should you encounter one. You can soft reset when you faint a legendary, but when you faint a shiny it's gone for good.

A Master ball is a very rare item that can usually only be given,

if you are thinking of using it on a lengedary then you should really reconsider as they can easily be caught as you can save before you get to them then retry as many times as you want until you capture it with (recommended) timer or quick balls

In my opinion MewTwo is a much harder pokemon to catch so if you were to use it it would be a better decision.

It is a better idea to use it on shiny pokemon that either flee or self-destruct so that if you encounter a pokemon that is really good, you won't regret wasting your master ball.

I think you should stock up on Quick Balls for legendaries. I used my Master Ball on Xerneas, so when I realized you could catch Mewtwo the only I had was a Quick Ball, and I only used one to catch it on the first turn. They're really useful. I think you should hold on to your Master Ball until you're in a tight situation

I suggest to use it on a level 2 magikrp,

rate 5 is u agree

Rate 4 if you disagree

I use mine on shinies. Legendaries aren't really legendary if there isn't a battle before capturing them... Just IMO

don't use at Xerneas

Lucky i caught Xerneas with pokeball @ 1 chance