Select a good Eevee as Buddy and Earn at least 70 hearts to Evolve. Daily hearts are earned through Giving Treats to Buddy (3x), Play together (1), Battle together (3x), Snaphot (1), Bonus (1) ~ 9 hearts. Tend to not earn any for the Walking (3x) and Visit a new place (1) tasks
Will have a choice to choose Sylveon to Evolve: the Silhouette with the Buddy sign
