The Pokemon Youtube Channel posted a trailer for those players who could remember some of the NPCs they’d like to encounter in Pokémon Legends: Arceus. The trailer was meant to show off the NPCs, which will operate the new clan system. There are two clans, the Diamond and Pearl. Man named Adaman, and the man named Irida is the leader of the Pearl Clan. According to the Pokemon Legends website, Adamans partners pokemon are a lefeon and Iridas are a Glaceon. Both characters have a different view and often baffle heads. Neither the trailer nor the website details the clans role in the story. We only know that they exist and are evidently referring to Dialga (Diamond) and Palkia (Pearl). The site mentions the mission for players that have the save file of Pokemon Brilliant Diamond or Pokemon Shinning Pearl. The mission is in the hands of the legendary Pokemon Darkrai and will let players catch them. Players can buy the Modern Team Galactic Set, a cosmetic that matches the outfits worn by team Galactics admins in Pokemon Brilliant Diamond and Shinning Pearl. Game Freak is doing that with a pokemon called Shaymin, but with more different games. If players possess copies of Pokemon Sword and Shield, they will receive a similar mission to Darkrai. Shaymin and Darkrai both appeared in the first Diamond and Pearl games. SOURCE
