Pokémon GO's buddy feature has a hidden easter egg if Pikachu is your buddy of choice. The buddy feature was recently launched as one of the more popular features in the game, which began hitting devices via a new update that started rolling out to users over the past few days, and was initially announced back on September 2nd. The easter egg, which isn't too terribly hard to discover if you play often enough (and even if you don't), follows the theme of a particular trait of Pikachu's from animated series, and for those who are loyal fans of the show this is one easter egg that is sure to be a delight.
If you're unfamiliar with the new buddy feature in Pokémon GO, what it does is allow you to select one of your Pokémon and label it as your buddy. From this point forward when you play the game you'll see your buddy Pokémon on screen with your trainer avatar, walking alongside you as you explore. The feature also lets your buddy Pokémon obtain candy as you walk and play which can then be used to help evolve them. If Pikachu is set is set as your buddy Pokémon, a short walk of 10km will then cause Pikachu to hop up onto your shoulder just as it did to Ash in the animated series time and time again. While this doesn't serve any functional purpose and won't grant you a bonus of any kind, it's a cool little nugget to be found if you grew up watching the animated series and played the original games.
The easter egg was discovered by The Silph Road which is a subreddit over on Reddit, and in addition to this easter egg the community is working tirelessly to discover plenty of other easter eggs and publicly advertise them to other players. While there have not been any others found just yet, it's entirely possible that it won't take long for more to emerge. Others are also contributing to ideas for easter eggs to find by posting in the thread comments, some of which the subreddit moderators are then listing as easter eggs which have already been checked out and if proven, labeling them as such. This is so far the latest easter egg to be found alongside another which allowed players to evolve their Evee's simply by naming them, and Niantic's CEO John Hanke has already hinted that there are more to be discovered, so players will definitely want to keep an eye out.