Pokemon Go is about to add over a hundred Pokemon over the next few months and it appears that some of them will need a special evolutionary item to evolve. Earlier this week, Pokemon Go announced it would begin adding Pokemon from Pokemon Black and White next month, giving players their first taste of Pokemon from the Unova region. Pokemon Black and White added over 100 Pokemon to the franchise, several of which evolve through the use of evolutionary items like Leaf Stones or Fire Stones. Since some evolutionary items aren't available in Pokemon Go, the developers came up with an alternative solution - the Unova Stone.
The dataminer Chrales confirmed that an upcoming update will have the Unova Stone, a new kind of evolutionary item. Similar to the Sinnoh Stone introduced earlier this year, players will likely use to the Unova Stone to evolve certain kinds of "Gen 5" Pokemon into their final forms. Although we don't know what Pokemon will need an Unova Stone to evolve, some likely candidates include Pansage, Panpour, and Pansear, three monkey-like Pokemon that need either a Leaf Stone, Water Stone, or Fire Stone to evolve. Other Pokemon from Pokemon Black and White with strange evolutions include Karrablast and Shelmet (which only evolve in the main series Pokemon games when traded for each other), Minccino, and Munna.
Currently, we do not know how players can obtain the Unova Stone or even when it will be implemented. While the Pokemon Go fanbase knew of the Sinnoh Stone in early 2019, the item wasn't released until late spring of this year. We also don't know whether the item will be a more common item like most Pokemon Go evolutionary items, or relatively hard to obtain like the Sinnoh Stone. You can see what the Unova Stone looks like below:
0.153.0 :— Chrales (@Chrales) August 22, 2019
new evolution item "Unova Stone" pic.twitter.com/MBh4d6H37Y