We have built up a list of CPs for the entire Community Day Pokemon, which, if fully developed, will result in their developed form with a CP that is within the requirement of 1500CP in the Great League or the 2500CP requirement of Ultra League in Trainer Battles. These Pokemon can have amazing moves, which is something we already wrote in depth: Pokemon GO December Community Day: Best Exclusive Moves to Look For. For more information on the recently published Trainer Battles, see our guide for everything we know so far.
If your unevolved Pokémon has a CP lower than or equal to those in the table below, it will be used in either Great or Ultra League when it is fully developed – the higher they are up to the given CP, the less they will require optimal optimization.
We recommend that you leave your evolutions as close to the event as possible if you find something worthy of sweets. But do not leave it too late ̵
1; Only Community Day Pokémon was developed before the end of the event will receive their exclusive features . See here for start and end times for the event in your region.
If possible, it would be advisable to get at least one <1500CP and a 1501-2500CP version of each developed Community Day Pokemon while they are still able to learn their exclusive features, as at least some of them are likely to be very relevant in the Trainer Battle League. At this stage, however, we can hold on to drive everything until we know the full mechanics of the Trainer Battles feature.
(Note that these ranges have not been calculated to half levels. See if you can pin another Power Up from the specific Pokémon (if it is useful) without exceeding the 1500CP or 2500CP limits for each league.  All CP values have been taken from the Pokémon Go Hub Database