For the very first time, GameFreak introduced Pokémon that evolve into legendary in Pokémon Sun and Moon. Cosmog is one of those Pokémon, the first stage of Legendary Evolutions. After leveling, it evolves into Cosmoem and then into your Version Box Legendary.
Please note that you still get one of the two Legendary Pokémon during the main story of Sun and Moon. However, in order to add the entire Cosmog evolutionary line to your Pokédex, you need to do this guide.
You can get only one secret Cosmog per copy of the game.
Secret Cosmog Guide
- You need to have completed the main storyline and became the champion
- Go back to the Altar of the [version you’re playing] and enter the portal
- Go to the Lake of the [version you’re not playing].
- Go to the top and onto the platform
- a cutscene will start and you will be able to add Cosmog to your party / box
Secret Cosmog in Picture
Cosmog Evolution Line
As noted above, your Cosmog evolves into Cosmoem and then into Sungaleo or Lunala depending on what version of the game you have.