Shedinja is finally returning to Pokémon GO the same way that it debuted… in the Research Breakthrough box. This may not be what trainers mean when they say they want this box to return to the Pokémon it used to offer, but this will certainly be a good chance for fans of the game who haven't yet been able to get this strange kind-of-evolution of Nincada in their Pokédex.
Shedinja will be the Research Breakthrough encounter starting Thursday, October 1st at 1 PM, and will run through Sunday, November 1st at 1 PM. This goes along with Niantic's 2020 change to these Research Boxes, which used to offer Legendary Pokémon but now reward non-Legendaries tying into the official Pokémon theme of the month. October is, of course, Ghost-themed. Because these themes come from the Pokémon Company and not Niantic, perhaps there is hope that once 2020 wraps up, the Research Breakthrough Boxes may return to their former glory.
One thing that's uncertain, though, is if Shedinja will be Shiny capable. The last time it was in the game, Nincada wasn't able to be encountered Shiny… but with it being released, it may be possible that the entire family, including Shedinja, may be Shiny. Notably, though, Niantic did not write their trademark "If you're lucky, you may encounter a Shiny _____" tease for Shedinja.
Besides this Shedinja re-release, other events for October include the previously announced Fashion Week and a Limited Research event featuring Meowth that will give tasks that reward encounters with not only the Kanto Meowth but the Alolan and the Galarian as well. This event will run on Saturday, October 10th from 8 AM to 10 PM local time. Niantic also teased an upcoming event celebrating their anniversary and the changing of the seasons that will run before their annual Halloween Event.