There is an interesting Pokemon in the game, the weather Pokemon called Castform. It has 4 different forms, which all have been released in Pokemon GO. There is the Normal form, the Sunny firm, the Snowy one, and the Rainy one. We must say that they are very cute and pleasing to the eye.
These forms do not have their own entries in the Pokedex, they fall under the Castform Pokedex entry. Each form of course has a different look to it, which can be easily linked to the weather its form represents.
The normal type of Castform usually appears in clear weather, cloudy weather, and windy weather. The sunny type can be encountered if there is sunny weather, the rainy one can be seen on a rainy day, while the snowy one can appear on snowy weather or foggy weather. Unfortunately, this Pokemon does not have its Shiny form released in the game.
You can also spawn Castform from Lures and Incense, also adopting the weather from which it originally appeared in.
At the moment none of their shiny forms can be found in the game, as they’re not released yet, but from a recent datamining, it has been reported that they’ve added Shiny Sunny, Shiny Snowy, and Shiny Rainy form in the GM file.
This is interesting, considering there isn’t a main series game with Castform Shiny forms. Their shiny is only in Pokemon Home.
This discovery could mean that they might be planning on a Castform event and we might see the release of Shiny Sunny, Shiny Rainy, and Shiny Snowy Castform forms.