In Pokemon Ultra Sun and Moon you can get Pokemon with Hidden Ability by the following method.
Wild Pokemon sometimes call for assistance when they’re in a losing battle. This trait has a higher chance of being activated after the 10th time a Pokemon has called for help.
Look at Pokemon who have learned Entrainment, Skill Swap and Worry Seed to check if they have learned a Hidden Ability
How to inherit Hidden Abilities
During Breeding, if a female Pokemon with a Hidden Ability breeds with a male Pokemon in a compatible Egg Group, the new born Pokemon will have a 60% change of obtaining the ability.
|Parent 1||Parent 2||Inherited|
|Hidden Ability ♀||Normal Ability ♂||Yes|
|Normal Ability ♀||Hidden Ability ♂||No|
|Hidden Ability ♂||Ditto||Yes|