Every Pokemon GO Community Day, an exclusive move for a Pokemon will be made available to all trainers if they evolve the designated Pokemon during the time of the event.
The next Pokemon GO Community Day taking place in April will have Ampharos know the special Dragon-type move Dragon Pulse when trainers evolve their Flaafy during Community Day.
Get charged up for #PokemonGOCommunityDay, Trainers! When you evolve your Flaaffy into Ampharos during Community Day, your Ampharos will know the special Dragon-type move Dragon Pulse! https://t.co/d9NW6wNEM5 pic.twitter.com/8kVsEsnaNN
— Pokémon GO (@PokemonGoApp) April 6, 2018