SOS Encounter: Poni Breaker Coast (30%), Seafolk Village (30%), Ancient Poni Path (30%, Only in Ultra Sun & Ultra Moon) + 1 more
Surf: Poni Wilds (10%, Only in Sun & Moon), Poni Breaker Coast (10%, Only in Ultra Sun & Ultra Moon)
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 Dive Ball, Net Ball or Great Ball.
Evolution: Wailmer → Wailord (Level 40).
Wailord in every game · Pokémon Sun, Moon, Ultra Sun & Ultra Moon interactive map (Alola)