When members of the Pokemon community on The Silph Road dug deeply into the latest version of the app (0.79.2), they discovered the new Halloween loading screen which reveals several generation three characters that are not currently in the game. Those pocket monsters include Dusclops, Shuppet, Banette, Duskull, and Sableye. We expect to see those five released during the Halloween event with the remaining generation three Pokemon appearing shortly thereafter.
While Niantic hasn’t said anything that specifically points to an upcoming release of generation three Pokemon, it has dropped a hint about catching new Pokemon to fill out your Pokedex. If past is prologue, we might see many trick or treaters show up at the door this Halloween with a bag in one hand, and their smartphone in the other.
source: TheSilphRoad via SlashGear