Not all of Alola’s legendaries are equal against Poké Balls. Solgaleo and Lunala let themselves be caught without much trouble, Necrozma almost too easily, but the four guardian deities are among the hardest Pokémon to catch in the whole series. Here is how to go about it.
First rule, valid for all of them: save right before the battle. If the Pokémon is knocked out by mistake or escapes from all your Balls, you can try again. Only Tapu Koko is an exception: the first battle follows on without any chance to save, but it comes back to the Ruins of Conflict if you defeat it.
Second rule: False Swipe and a status condition. A Pokémon at 1 HP, asleep or paralyzed, is much easier to catch. Sleep is the most effective.
