I just came up with that one for the Dark Armour ending. If Serenity comes in with the Dark Armour, Aidan asks what Ataraxis is doing before realising its Serenity. He then laughs before gloating over how he can mind control anyone wearing a gasmask and if Serenity was aware of this. Serenity is taken by surprise before the mind control takes effect and the ending has Serenity replace Ataraxis. It's implied that several more people tried to stop Aidan only to be slain by Serenity Horton.

If Serenity is wearing a different costume with a gasmask, Aidan just gloats, Serenity is surprised and gets mind controlled, and the ending is the same as the original Lunar Shadow's Betrayal Ending.

Dark Armour = The New Ataraxis Ending
Any costume with a gasmask = Betrayal Ending