Use a Lucky Punch on Chansey to evolve it into Blissey in the main series games
In Pokémon GO, Chansey does not evolve directly; evolve Happiny into Chansey, then use 50 Chansey Candy to evolve Chansey into Blissey
In Pokémon Legends: Arceus, Chansey evolves into Blissey when leveled up with high friendship
In Pokémon Scarlet and Violet, use a Shiny Stone on Chansey to evolve it into Blissey
In Pokémon Sword and Shield, use a Shiny Stone on Chansey to evolve it into Blissey