AoM Headcanon (?? because I lost count)
Sarx will be the one that backstabbed Morningstar and took over LEGION-- not Minister of Lust, nor Wrath, nor Greed, nor even Lucas Brimstone. Her betrayal will shocked everyone, that even Persephone Brimstone herself (the first traitor) surprised once the news came to her.
No one expect the quiet one. The scheming Serpent. The one standing in the background.
It was kinda stupid tho for not letting Ministry of Sloth to have their own troopers and let Sarx (the shapeshifter) to do her own thing without any extra surveillance. Where the hell do you think Persephone got her intel regarding Morningstar's true ambitions? Sarx. (Hence why Persephone refused to elaborate further about who was her source). Why Sarx tried to recruit Scheherazade, someone from outside LEGION (and someone that she knows obviously from her past)? What exactly she was doing during the events in AoM?
What if all along, all those events were orchestrated by Sarx? She gave Persephone enough info to pit her against Morningstar. She was the one who whispered falseness on her ears so she would doubt her own husband's intention to the point that Persephone had to leave her husband to his own death. Sarx manipulated Doctor Babylon through strings of failure/sabotage around his Ministry to the point that he started to believe that Morningstar had begun to doubt his own worthiness.
Persephone and her MAYHEM were unknowingly ones of Sarx's many little pawns, along with the other Sin Ministers and LEGION-- and perhaps Morningstar himself.
Nobody knows Sarx whereabouts. Until it's too late.
By then, everyone played their roles in their designated positions, exactly as Sarx planned. She doesn't care if this will doom everyone or destroy her own people.
After all, Sloth isn't just about laziness.
The greatest sin that even God fears it.
And Sarx was never the one that faithful toward Morningstar in the first place.