It appears that a new Mythical Pokemon will be added to Pokemon Go in the coming weeks. The popular dataminer Chrales posted on Twitter that new quests for the Mythical Pokemon Jirachi were added to the game's code in a recent update. While no other details were given, it's likely that the Mythical Pokemon will be added to the game similarly to how Celebi was introduced at Pokemon Go Fest 2018. After all, Pokemon Go Fest 2019 is less than two weeks away, and it makes sense that Niantic would give attendees early access to a new Mythical Pokemon quest before other players. Last year, Pokemon Go had a quest in which players who attended Pokemon Go Fest could obtain Celebi and then a second quest in the fall for other players.
Jirachi is known as the "Wish Pokemon" and was originally introduced in Pokemon Ruby and Sapphire as one of two "Gen 3" Mythical Pokemon A Psychic/Steel-type Pokemon, Jirachi is based on the idea of "wishing upon a star" and appears once every thousand years to grant wishes to those who attaches a note to its head. In addition to its unusual typing, Jirachi is the only Pokemon in the main series games that can learn the move Doom Desire, a move that deals damage two turns after it is used.
In addition to the teases of a new Mythical Pokemon, Chrales also noted that two new moves were added, including the Fairy-type Fast Move Charm. There is currently no Fairy-type Fast move in the game, so Charm has the potential to be a game changer. In addition, the next loading screen will change based on the time of day, with a different color scheme depending on when players open the game.
We'll have more details about Jirachi and other Pokemon Go updates as they're announced.