Cartoon Network / The Pokemon Company
Certain Pokémon that are currently in the game, like Eevee and Seadra, will be able evolve into unreleased second-gen Pokémon from the original game's Johto region.
"Pokémon Go" creator Niantic Labs has revealed that you'll need special evolution items from Pokéstops to evolve some creatures from the game's first generation into their second-generation counterparts. But you'll also want to stockpile candies now from existing Pokémon so you can power them up once they're evolved.
We've used data complied by the Pokémon Go experts from The Silph Road on Reddit, Bulbapedia, and official creature descriptions from the master Pokédex to put together the following list: