Two Pokémon as rare as they are popular, Shiny Pikachu and Mewtwo, recently showed up for Pokémon Go players in Japan. Players in other regions need not feel left out, though, because everyone will soon have the opportunity to try their hand at catching them.
First, Shiny Pikachus might already be showing up in your area. After about a week of only appearing in Japan, the rare variant of the popular creature has started to show its shiny little face around the world. The only substantial differences between a regular Pikachu and its shiny version are sparkles on its Pokédex page along with a darker, more goldish color.
Like other legendaries, capturing Mewtwo will require participating in a Raid, however this time it will be a little different. Mewtwo will only appear in Exclusive Raid Battles that require an invitation to participate in. To earn an invite, you have to complete a normal raid at the same gym the exclusive event is scheduled to take place at. Raid Eggs received from these battles will also contain more powerful Pokémon than normal.
Pokémon Go has seen quite a few significant updates recently alongside some significant roster expansion, especially when it comes to legendaries. If these most recent developments are any indication, it looks likely this trend will continue.
Source: Nintendo Everything 1, 2