Jigglypuff is known to use the move Sing, which causes Pokémon to fall asleep. It evolves into a Wigglytuff via a Moon Stone. It is rare, yet it has a high catch rate of 255, meaning it can be caught with a Poké Ball easily. Therefore, if you have a Jigglypuff in sight, it is recommended you catch one using a Poké Ball or a Great Ball.
In addition, Jigglypuff's evolved form, Wigglytuff will not learn any moves through leveling up so you may wish to level up your Jigglypuff to learn some decent moves before using a Moon Stone on it.