#gloomtail

1st set of Shadows in the first: Reside in Cognitive Plane Area Somnabula, or as it's better known in reality, Pi'illo Island. Since Zeekeeper is the guardian deity of this island, he takes the benign version of the role of Yaldabaoth in that Zee advocates more for freedom of the hearts in his world (whereas Yaldabaoth set it upon himself to control humanity's desires to his liking in the form of Mementos, aka, the Prison of Regression.) The Somnabula does not have a set Palace Ruler because of Zee's role as dream god, which leaves Shadow Selves to blossom a bit more freely and be able to truly return to the Sea of Souls without any further problems once issues are resolved. 

2nd set of Shadows: Reside in Dreambert's Palace, or what is referred to as the Castle of Purgatory, the true mythical form of the Shadows being like that of Smouldergeist. Palace Ruler is Dreambert, who sees himself as a Nightmare for his actions against Antasma, believing himself to be no better. The Demonic form of Shadow Dreambert doesn't have a true name, but the presence of the needle through the chest implies some manner of heartache/break. The shackles present on both forms seem to represent feelings of being trapped/imprisoned by the pain of his actions towards Nightmares as well as his responsibilities as king which he feels he's failing at. 

3rd and 4th set of Shadows: Reside in Mario Bros' conjoined Palace, what is referred to as the Castle of Troubled Brotherhood. The Shadows here, when masked, resemble that of Toads. The Red Toads appear more combat ready, while the Green Toads appear dressed as servants or look like puppets. The Palace Rulers are Mario and Luigi themselves. 

Shadow Mario sees himself as a strong war hero, and as such, finds himself in no need for a demonic form. Shadow Luigi is almost the opposite, seeing himself as Mario's grim shadow. He actually has a demon form resembling a three-headed dragon that alternate control depending on Luigi's personality.

The leftmost head is reminiscent of Fracktail in terms of facial appearance and represents the villainous side of Luigi's personality known as "Mr. L", while the rightmost head is reminiscent of Gobblegut and Hooktail/Gloomtail simultaneously and represents the miserable and depressed side of Luigi's personality referred to as "Game Over", in reference to the beta bad ending for the original Luigi's Mansion. The center head resembles that of Dragohoho and I can only assume this head is representative of the happier and kinder Luigi we all know and love,