With the Hatchaton event active, Niantic has apparently also added the Sinnoh Stone into the game. Which is used to evolve 11 Pokémon into their generation 4 Sinnoh evolutions. The majority of these Pokémon require a different item for them to evolve. Which must be why Niantic has decided to release a new evolution item called the Sinnoh Stone. So that we don't get too many different evolution items in the game. This way we can also choose which of those Pokémon to evolve with the item, rather than having to wait until we get a certain Pokémon's specific item.
The Sinnoh Stone is received from the Research Breakthrough reward box for now. I haven't heard of any other ways to get it yet. I do assume it'll be available from Pokéstops and Gyms as well and from the 7-day streak for spinning a Photo Disc. If that's the case it's just not guaranteed due to the other evolution items. The one from the Research Breakthrough reward box is guaranteed though.
With the Sinnoh Stone, the following Pokémon can now evolve into their gen 4 evolution:
- Electabuzz -> Electivire
- Magmar -> Magmortar
- Rhydon -> Rhyperior
- Porygon2 -> Porygon-Z
- Sneasel -> Weavile
- Murkrow -> Honchkrow
- Misdreavus -> Mismagius
- Togetic -> Togekiss
- Gligar -> Gliscor
- Roselia -> Roserade
- Dusclops -> Dusknoir
All of these require 100 of their respective Candy to evolve. I'm currently debating between my Rhyhorn and my Sneasel for which one I'll evolve first.
Which Pokémon will you evolve first with your first Sinnoh Stone?