Walk: Pokéwalker
Its base catch rate is 150 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 Love Ball, Heal Ball or Moon Ball.
Evolution: Cleffa → Clefairy → Clefable (Moon Stone).
Cleffa in every game · Pokémon HeartGold & SoulSilver interactive map (Johto & Kanto)