Chaining backup calls in a single battle is the most powerful technique in Sun and Moon: as the chain grows, the Pokémon called have more perfect IVs, more often their Hidden Ability, and a better chance of being Shiny. Here is how to build and sustain a long chain.
The principle: you keep the original wild Pokémon alive, knock out every ally it calls, and start over. Each ally called extends the chain by one.
The rewards increase in tiers. They only apply to the allies called, not the original Pokémon.
