My first thought for the December Community Day was that it would feature Trapinch or Bagon. As we had Beldum between Chikorita and Cyndaquil. Though it seems like this won't be the case at all. Because all of the 2018 Community Days' Pokémon will be featured in a special December Community Day weekend!
From Friday November 30 through Sunday December 2, we will see increased wild spawns of Bulbasaur, Charmander, Squirtle, Pikachu, Eevee, Dratini, Chikorita, Cyndaquil, Mareep, Larvitar and Beldum all weekend long!
There will be a special bonus available during the regular Community Day 3-hour time window on December 1 too. This special bonus gives us double catch XP, double catch Stardust and double Incubator speed. So that time would be really great to head outside to make the most of the Community Day weekend.
If you've missed any of the Community Day Pokémon from anytime this year, then that weekend will surely be a great time to go out there and look for the ones you missed. There has been no message about the special moves that have been available during each Community Day though. We'll most likely get to hear whether or not those become available again close to the start of the event.
I didn't have a lot of time during the Bulbasaur and Mareep Community Days, so I'll be sure to look out for their Shiny more than any others, but won't neglect any though! That will also be a great time to get some more Beldum Candy so that I can consider powering my two Metagross up more.
Which Pokémon of the 2018 Community Days are you looking forward to the most to catch during the special December Community Day weekend?