Pokémon GO developer Niantic has announced that Field Research in December 2018 includes previously-featured Pokémon. In addition, Articuno, Zapdos, Moltres, Raikou, Entei and Suicune will officially return as Research Breakthrough rewards. December Field Research will go live on December 1 a 1 p.m. PDT. The official announcement from the development team is as follows:
Get ready, Trainers. Field Research in December brings some previously featured Pokémon back into the spotlight! Every time you reach a Research Breakthrough during the month, you’ll have a chance to encounter Articuno, Zapdos, Moltres, Raikou, Entei, or Suicune!