FusionDex

Koffpuff is timid by nature and prefers solitude. If overheard while singing, it panics and secretes poisonous gas from its skin, a habit that causes other Pokémon to keep their distance.

Nothing can avoid falling asleep hearing a Koffpuff's song. Getting up close to a Koffpuff will give you a chance to observe, through its thin skin, the toxic gases swirling inside.