The iOS App Store has put up a picture of a brand new Halloween Hat Pikachu and other Generation 3 Ghost-type Pokemon to promote Pokemon GO.
The featured image no doubt confirms that these Pokemon will be released in one way or another during Halloween in Pokemon GO.
The first Generation 2 were rolled out in slow and gradual steps, starting with baby Pokemon. Thus the Halloween season is Niantic’s way of rolling out Generation 3 Pokemon, starting with Ghost-types.
Earlier this year, before the reveal of the Legendary Pokemon, the App Store uploaded a picture promoting the first Legendary Pokemon in Pokemon GO. So this pretty much confirms it will be a matter of time before The Pokemon Company and Niantic officially announces their Halloween campaign.