Pokemon GO's Special Research quests are the only ways that players can get some of the rarest Pokemon in the game. Mythical Pokemon like Mew, Celebi, and Jirachi are only obtainable once Pokemon GO players complete a series of Special Research tasks, but sometimes they get stuck on a task for one reason or another. When it comes to the Jirachi Special Research, one task that seems to be giving some Pokemon GO players trouble is catching three Whismur.
When the Jirachi Special Research quest first started in Pokemon GO, Whismur was an extremely common Pokemon to find out in the wild. In fact, Whismur was about as common as a Rattata or Pidgey back in the Gen 1 days, and so it stands to reason that a great portion of Pokemon GO players have flown by that particular task in the Jirachi Special Research. However, Whismur has become a bit more difficult to find since then, so players who take their time with Special Research may be struggling to move on to the next page of tasks.
Unfortunately, there really is no surefire way to catch Whismur. At the time of this writing, none of the Pokemon GO research tasks result in a Whismur encounter, so players can't even go hunting for Field Research tasks to make things easier. Really the best bet is for players to wait a bit, as Whismur's spawn rate is likely to increase in a few months.
Right now, Pokemon GO is in the midst of the World Tourism Day event, not to mention the recent addition of the first Gen 5 Pokemon. These revelations have muddied the Pokemon spawn pool a bit, making it more difficult to find Whismur than it would be otherwise. Eventually, Pokemon GO will stop spawning Gen 5 Pokemon at such a frequent rate, and it will enjoy a period of time with no event Pokemon as well. That's when Whismur's spawn rate is likely to increase, so for Pokemon GO players hoping to catch three Whismur, it's just a waiting game at this point.
Pokemon GO players may have to wait until November for Whismur spawns to increase, as the annual Halloween event is likely to take up the bulk of October, meaning players will mostly find ghost-type Pokemon out in the wild. Whismur will return, though, and maybe there will even be a special event that increases its spawn rate, too.
Pokemon GO is out now for iOS and Android mobile devices.