What to use masterball on?

What should i use my masterball on if u even should use it at all? (im currently doing the arceus guest thing)

Yeah, Arceus is a good candidate for a masterball imo. I caught almost every other legendary with either a timer ball or a heavy ball.

Ill see what i do when it comes to that time

Arceus, Genesect, Meloetta, Azelf, and Volcanion are all good candidates for using a masterball on as they all have a way to kill themselves.

Up to you obviously, but I used them on the random encounter ones. Raikou, Entei, Suicune, & Cresselia. (I got lucky and got another Masterball from the Sonata Tracks, but keep in mind you only get 3 from the actual game!)