Niantic have announced the details for the 18th Pokémon GO Community Day which takes place on July 21st, 2019 at 4:00 PM until 7:00 PM EST. The featured Pokémon for this day is Mudkip. Mudkip will appear in the wild more frequently for three hours that day. If you evolve Marshtomp into Swampert during the three hour window, your Swampert will know the charge move, Hydro Cannon. The 3x Catch XP and 3-hour Lures bonuses will also be available that day.

Source: https://pokemongolive.com/events/community-day/

Mudkip Promo Clip

Original Source: https://twitter.com/PokemonGoApp/status/1143929848173215744