The Shadow Triad is a group of three ninja-like Team Plasma subordinates that are only loyal to Ghetsis. They don't appear to have any feelings, which is evident at N's Castle when one of them says a bit about N's Playroom, and says that he doesn't feel anything at all when he goes in there.
They make one final appearance after the defeat of Team Plasma; when the player has access to the new areas of the Unova region, the trio will appear on the Marvelous Bridge near Nimbasa City and inform the player that Ghetsis has gone off to another region to rethink his plans. Before departing, they gift him/her with the Lustrous Orb, Adamant Orb and Griseous Orb - the three items that power up Palkia, Dialga and Giratina respectively. They explain they gave the player these items as it was their master's wish. They depart, wondering what to do as Ghetsis has relieved them of active duty under him after this task.
In Black and White Versions 2, they can be battled during the main course of the game as they once more serve under Ghetsis. They first appear when Zinzolin summons them to kick the player, Hugh and Cheren out of the Plasma Frigate. They claim they don't serve him, but Zinzolin claims he knows but asks them once more to kick them out, which they do. They are seen later after Team Plasma freezes Opelucid City as they are looking for the DNA Splicers, a tool linked to Reshiram, Zekrom and Kyurem. After the Team Plasma forces are defeated. Drayden reveals the true location of the DNA Splicers, being hidden on the Gym and gives the tool to the player. However the Shadow Triad appears revealing they were using Zinzolin and the other Plasma grunts waiting for the proper chance to steal them, which they do. Drayden and the player give chase, and one member is battled. However that member was only buying time for the other two and retreats. The Shadow Triad is later mentioned by Rood as being the likely hosters of the Purrloin that Hugh has been looking for. Eventually after the player defeats Colress and meets Ghetsis, the Shadow Triad informs Ghetsis that Kyurem has been moved successfully and departs, while the trio confront the player and Hugh, confirming that they in fact had the Purrloin robbed to Hugh's sister, however and much to Hugh's surprise it has evolved into a Liepard. After their defeat, they hand over her Liepard as they have no need for it. After Ghetsis is defeated and loses control of himself, they take him with them and dissapear. The are later found and can be battled and re-battled in Icirrus City seeking revenge on the player as they mention Ghetsis will not and cannot do any more harm (suggesting he's sick or greatly injured), and claim that only defeating the player will bring joy to Ghetsis. They can be rematched every time the season changes, but be aware, refusing to battle the second or third Shadow will mean you have to wait until next season.
If Memory Link is used, it is shown in a flashback that they challenge the Gym Leaders of Stration City Cilan, Chili and Cress on a "whim" as the trio of Gym Leaders who began questioning their strength find it the perfect chance to prove themselves. The Shadow Triad however easily overwhelms them and they depart to check onto other Gym Leaders so that they cannot be a threat to Ghetsis. The humiliating defeat however makes the trio of Gym Leaders to resign their position to start their training from scratch.
In the Pokémon Adventures manga, they are first shown speaking to Ghetsis.
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The Shadow Triad is irrevocably loyal to Ghetsis, because he once saved all three of their lives.
Their manga appearance is quite similar to the appearance of Mello from the anime/manga series Death Note.
There was a popular fan theory since the release of Black and White that they are the Striaton Trio; this is not true because in the flashback in Black 2 White 2, A Triple Team it shows the Striaton Trio battling the Shadow Triad.
In Pokemon black 2 and white 2, it is mentioned that they have powers to immobilize people