Niantic revealed that when it comes to a Pokemon GO Detective Pikachu tie-in, it is on the case. From May 7-17, 2019, the mobile game will be celebrating the movie. That means new Field Research missions, certain Pokemon will appear more often, and new avatar items.
When it comes to Pokemon, ones that have major roles in Detective Pikachu will show up more often. That means you should keep an eye out for extra Aipoms (both standard and shiny), Bulbasaurs, Jigglypuffs, Psyducks, and Snubbulls. Some detective hat-wearing Pikachus will appear, showing up to photo-bomb a Snapshot. If that happens, you then have a chance to catch it. Double XP will be doled out for every Pokemon caught.
As for activities, a few are planned. Both Field Research missions and Raid Battles inspired by Detective Pikachu will appear. No Pokemon were specifically named for these events. People will also be able to buy a themed hat and t-shirt for their avatar from the Style Shop.
Pokemon GO is available for Android and Apple iOS devices.