Following the latest update for Pokemon GO, players can now choose one of their Pokemon as a buddy that appears alongside their Trainer avatar on their profile screen. If you select Pikachu as your Buddy Pokemon and walk at least 10 kilometers, it will hop on your shoulder when you view your Trainer details screen. Of course, this is a nod to the bond between Ash and his Pikachu in the anime.
Pokemon GO Easter egg enables Pikachu to ride on your shoulder
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