With Terapagos being featured on the Indigo Disk DLC cover art, it's no secret that every PokéTrainer had their eyes set on the Pokémon right from the get-go. Adding the Pokémon to your Pokédex, on the other hand, is a different story. Because the Terapagos is a Legendary Pokémon, defeating and capturing it will put trainers to the test. Nonetheless, the Terapagos is one Pokémon in this DLC that's well worth the effort.
Warning: The following article contains spoilers for Pokémon Scarlet & Violet Indigo Disk DLC.
The good news is that catching a Terapagos is not a game of luck or chance; everyone is guaranteed to encounter and catch the Legendary Pokémon as it is tied to the main story. Therefore, it's just a matter of hitting some milestones in the story before you get your chance to catch a Terapagos, much like how you find and catch Iron Boulder in .
You can't start your encounter with the Terapagos until you have first defeated all four BB Elite Four Trials. Following that, you need to fight and beat BB League Champion Kieran as part of the story. After this battle, Ms. Briar will invite you, Carmine, and Kieran to explore a new part of Area Zero. This is where you will encounter the Terapagos for the first time in DLC.
Once you take the elevator down from the Lab, explore the area until you see some crystals blocking a doorway and some glowing Pokémon (Stellar Tera Type form) nearby defending it. Just past this point, Keiran will pull out a crystal that will transform into a Terapagos. Kieran will then pull out a Master Ball, catch the Terapagos, and challenge you to a fight.
After you come out on top in this fight, a cutscene will play in which the Terapagos escapes its Master Ball, Terastilizes, and challenges
Read more on screenrant.com