Happiness is a feature that allows certain Pokemon to evolve.
While there is no way to track the exact happiness points of the Pokemon players are training, players can see that hearts will start to appear in the Pokemon's information. To see any Pokemon's information, players have to click its name to open the Pokédex. Hearts will appear as a Pokemon's happiness level is raised. The happiness will rise displaying one of four hearts: 
- A Pokemon needs 73 points to gain a heart. The exception is the last heart, which only takes 35 points.
- All Pokemon that need happiness hearts to evolve need 3 hearts (220 points). The exception is Sylveon, which needs 4 hearts (255 points). Sylveon is the final evolved form of Eevee.
- Since happiness points per battle is randomized (1 or 2), players would need somewhere between 37 to 73 battles in order to gain 1 heart for your Pokemon.
- Happiness is not reset when a Pokemon is traded.
that be some fire anal