Blissey senses sadness with its fluffy coat of fur. If it does so, this Pokémon will rush over to a sad person, no matter how far away, to share a Lucky Egg that brings a smile to any face. This kindhearted Pokémon nurses sick Pokémon to health. It senses feelings of sadness. The eggs it lays are filled with happiness. Eating even one bite will bring a smile to anyone.
Pokédex entry #242
Blissey in Pokémon GO
It's possible to hatch Blissey from an egg?
No, Blissey can't be hatched.
Which are Blissey’s strengths and weaknesses?
Blissey is a normal type Pokémon. normal type pokémons but weak against rock pokémons. They are not affected by ghost type pokémons.