The following spawns are currently boosted:
• New Alolan Pokemon - Alolan Geodude, Alolan Diglett
• New shinies - Minun, Plusle
• Weather specific - Lotad, Cacnea, Snorunt
• Biome specific - Swinub, Magmar, Seedot, Wailmer, Feebas, Slugma, Aron
• Gen 3 starters - Treecko, Mudkip, Torchic
• Rare ones - Alolan Exeggutor, Aerodactyl, Trapinch
It has also been confirmed via GoFest that you can do both the Mew and Celebi field research tasks at the same time, so for those still on Mew, don’t worry - it won’t go away!