How do you get a blissey in crystal?

To get a Blissey in Pokémon Crystal, you first need to evolve a Chansey, which is the pre-evolution. Chansey evolves into Blissey when it levels up with high friendship. To increase Chansey's friendship, battle with it, give it items like vitamins, and use it in contests. Once its friendship is high enough, level it up, and it will evolve into Blissey.