History NightmareFuel / AMothToAFlame

* Lady Olivia tries to plead for Marcy to pull a HeelFaceTurn, Marcy gently brushing her hand off out of remaining fondness for her Newt friend... Then she spitefully tells her and General Yunan that the [[ThatManIsDead Marcy they knew]] '''[[ThatManIsDead is dead]]'''. Yunan considers the teen BeyondRedemption after hearing this from her.

* When Marcy wakes up in Chapter 14, even King Andrias is cautious around her unhinged demeanor, blaming her former friends for her near-fatal injuries for not joining her in conquest and vowing {{Revenge}}.

** In particular, her hideous drawing of the Core which Grace described as looking like an EldritchAbomination. It gives similar vibes to the darker and more crude pages of ''Literature/GravityFallsJournal3'', except instead of being terrified of the BigBad of the story, Marcy seems to be ''addicted'' to its influence and [[DrunkOnTheDarkSide doesn't want the wonderful feeling it gives her to stop]].

* In Chapter 2, the mural Sasha and Grime find depicting King Andrias standing over the bones of his enemies with his master in the background shows the plans he has for other worlds, and it isn't pretty, just like in the show. In story, it also includes ''human beings'' that used to live in Amphibia, the inscriptions were engraved along the bottom foreshadowing Marcy's role in the story, something Sasha figures out.

* Chapter 17 provides a look at Marcy's journal, [[ThroughTheEyesOfMadness giving us a look at her descent into corruption and madness in her own words]], detailing how she goes from a cheerful child overjoyed at her Isekai adventure to an insane would-be MultiversalConqueror, much to her parents' horror. The early journal entries give way to unhinged, unpunctuated scrawls once the Core gets involved, especially when Marcy to starts madly ranting about things that aren't going her way. In hindsight, it seems Lady Olivia was right about Marcy wearing a MaskOfSanity for the past month that came off in the throne room.

* Lady Olivia tries to plead for Marcy to pull a HeelFaceTurn, Marcy gently brushing her hand off out of remaining fondness for her Newt friend... Then she spitefully tells her and Yunan that the [[ThatManIsDead Marcy they knew]] '''[[ThatManIsDead is dead]]'''. Yunan considers the teen BeyondRedemption after hearing this from her.

* When the Core finally arrives and reveals itself to the four, Gernal Yunan tries to attack it. An angry Marcy goes to its defense SuddenlyShouting at her to get away from her master. Her MadnessMakeover is described as having [[EeriePaleSkinnedBrunette discolored skin]] with [[CreepyShadowedUndereyes sunken cheeks and eyes]], along with an AngryAnimalisticGrowl and a DeathGlare. Backing off, Yunan calls it a sight more haunting than [[MechanicalAbomination the Core]].

** In Chapter 13, Marcy is given her own perfect world inside her mindscape, complete with copies of Anne and Sasha who [[YesMan mindlessly adore her]]. However, as her final test, the Core creates an army designed to destroy it, driving [[GainingTheWillToKill Marcy to kill the entire army]] in various brutal ways, from hand-to-hand combat with SuperStrength to [[ImpaledWithExtremePrejudice impaling them with rock spikes]] and killing the last one with a FinishingStomp. She does this with no mercy, feeling proud of it, going so far as to give an EvilLaugh, and fully cementing her descent into evil, to the Core's approval.