SOS Encounter: Route 12 (15%, Only in Ultra Sun & Ultra Moon), Blush Mountain (15%, Only in Ultra Sun & Ultra Moon), Poni Plains
Walk: Poni Plains (20%)
Its base catch rate is 60 out of 255 (higher is easier); the catch rate calculator works out your odds with each ball. For the look, the best colour match is Repeat Ball or Timer Ball.
Evolution: Mudbray → Mudsdale (Level 30).
Mudsdale in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)