As of Thursday, January 18th 2018, The Pokémon Company International declared 2018 to be the “Year of the Legendary Pokémon”. This means that there will be various distributions of legendary Pokémon throughout the year.
The Pokémon that get distributed aren't mythical Pokémon, but luckily 2017 was the 20th anniversary. In celebrating the occasion, they distributed mythical Pokémon throughout the year. This year they chose for a similar scheme, but the legendary Pokémon you receive depends on your game. (e.g. Ultra Sun or Ultra Moon) Additionally, this marks the first time that Shiny Zygarde is being officially recognized by TPCi, and to be slated for release in June.
Pokémon distribution schedule:
- Sun/Ultra Sun: Palkia
- Moon/Ultra Moon: Dialga
- Shiny Zygarde
Some of them come with a gold bottle cap. They are at least level 60, and know "awesome moves", according to TPCi.