Along with the Unova Celebration Event currently live in Pokémon GO, Niantic introduced a brand new challenge for trainers to complete. Here is everything there currently is to know about Collection Challenges in Pokémon GO.
The basic premise of Collection Challenges in Pokémon GO isn't much different from Timed Research tasks. To access a currently live Collection Challenge, go to the Today View where Timed Research is located. There, you will see the challenge, which challenges trainers to catch a specific collection of Pokémon. All of the species' sprites are pictured there and, when one is caught, trainers are alerted that they've made progress the exact same was as with Research. Trainers must catch just one of each tasked species in order to complete the challenge.
This feature debuted during the Unova Celebration Event, and it was easy to complete. So easy that some trainers wondered why it was there at all, especially considering the unimpressive rewards given. Personally, I believe that this was purposely simple as a trial run for something bigger.
Based on what we know about the upcoming Pokémon GO Tour: Kanto, this new feature will likely come into play. In a previous announcement, Niantic revealed that trainers would be tasked with catching every single Generation One species during the event. While the event is confirmed to have Special Research, I think we can safely say that catching every Kanto species will be done as a Collection Challenge. In fact, I'd be willing to bet that this feature may have been created specifically for that event. Think about it. If "Catch Every Kanto Species" was a task on a page of Special Research, trainers would be stuck on a single page for likely the vast majority of the event. This feels like a clever way to separate that kind of task from Special Research to facilitate trainers in advancing through other tasks while working on a larger goal.