Promotional EventsLike so many other mobile games, Pokemon GO runs a number of promotional events from time to time to try to get more players playing or current players an added incentive for continuing to play. Usually, Niantic corresponds these events with holidays celebrated around the world, as well as some commercial holidays celebrated in given regions of the globe. Holidays such as Valentine's Day, Thanksgiving, Halloween and Christmas have all previously had a Promotional Event (and they continue to year in and year out).
During these promotions, there is usually some sort of enhancement to gameplay during a given time frame. Normally, this is either Double Experience Earned or Double Pokemon Candy Earned, but it isn't limited to only those given factors. During a previous Christmas Promotional Events, Pikachu could be found wearing a special hat to commemorate the event. During a former Thanksgiving Event, the Kanto Starters spawned more often; during previous Valentine's Day Events, Pink Pokemon (and later Luvdisc) appeared more. There was even a promotion that gave one Egg Incubator to players every day during the event by spinning PokeStops! Most Promotional Events also sees item bundles available for discounted prices in the Shop!
Player should definitely keep an eye out for upcoming events for Pokemon GO, as it usually sees them cashing in on loads of incentives otherwise unobtainable.