Ok, I've been sitting on this since November, but wanted to wait until Marcy's Journal came out, then said I would post this by February and now it's March, so screw it! I also plan to post this to my AO3 account, but getting the tags sorted is kinda intimidating, so I'll just crosspost it when it's up. Also, I got a bit annoyed by the "Amphibia characters get inserted into the FNAF story" and this idea was more of a blend of the two worlds.

NOTE: I'm not exactly as familiar with the FNAF canon as with the Amphibia canon, so some of the stuff in here may just be made up/nt entirely canon-conforming. Now, the synopsis of this idea: What if the Core used Remnant to revive Marcy into a robotic body?

For some explanation, Remnant is a substance in FNAF that comes from the suffering of children and is used to give non-possessed animatronics life or strengthen already living/possessed beings.

Now for the timeline I wrote up: The FNAF timeline goes as normal on Earth, while at some point during the Newtopian Imperial Era, the Core discovers Remnant and uses it to not only enhance the Frobots, but improve the brainpower and cohesion of the Core. Much later on, when Marcy gets stabbed, the Core gets an idea. Sure, they could just puppet Wit basically as is, but she is a child, and they would like a different host to the overly sentimental Andrias. Why not let her original body die, store her soul in a new body and when Wit moves with its attached soul, it'll become more easily manipulable by the Core when they move in?

This part is especially "handswavy", but somehow, the Core also makes a copy, fleshy body that can swap between the robot body in a dimensional space, with the idea of using it for spying purposes and for tricking Heart and Strength into thinking "Marcy" is just as weak and human as before. That body is the one we see from Olivia and Yunan and beyond. As a result, when Marcy gets freed, everyone thinks that thanks to miraculous Newtopian tech, the spinal injury was healed up with some scars and the temporary green blood (an illusion for further deception).

Cut to the timeskip and apart from some nightmares of Darcy laughing, or old animatronics from the defunct Fazbear Entertainment leaking blood while children scream (because Marcy technically died, she can share her dreamspace with the memories of those Afton killed), everything seems fine for Marcy. She's got two amazing girlfriends, her art streams are going well and they're just going to meet a family friend of Sasha's, Vanessa Emily. (Yes, in this AU Vanny is related to Henry Emily) Unbeknownst to the trio, Vanessa is recovering from a time of being possessed by Glitchtrap, which has left her with the ability to see through Remnant powered illusions, which the "human" body Marcy is wearing counts as...

Now, for some of the more miscellaneous details, starting with the mechanical body. The way I imagined it was, why would the Core make some animatronic form, when it wanted to conquer the multiverse with this body? It would want something that conveys strength and power, built for war and not entertainment. I imagine it looking like Darcy, but more thickset, like a slimmer and taller Grime. The armour covers the whole body and extends into a tail with retractable thagomizers. It also has an ability to manifest small, nail-like versions of the flame scythe from the fingertips. It can climb walls and go invisible for short periods of time.

Some smaller ideas: Vanessa is in LA to hunt down Glitchtrap, who reports indicate is still out there and working with a new ally, who the only thing known about them is a name: The Core (when Frogvasion was happening, Darcy uploaded a portion of the Core to the internet as a backup/way to further disadvantage Earth defences. It stayed hidden when the invasion fell and later on ran into Glitchtrap)

Yes, Sashannarcy is a thing. If you want to pick this up, it doesn't matter if they've been together for a while or have just admitted their feelings to each other.

An alternate, manga style title I had was "Now 2 Members Of The Calamity Trio Have Existential Dread!" for obvious reasons.

A power that Marcy could have is the ability to interface with and alter the code of Remnant enhanced robots, as the Core would've viewed this as an easier way to control the Frobots. An interesting side effect of this that isn't entirely plot necessary is: Marcy finds a discarded Fetch dog, accidentally fixes the murderous elements of its code, keeps it when she hooks up with Anne and Sasha and Vanesa freaks out when she visits their place and sees a Fetch just casually living with them.

And that's all that I wrote up. I'm good at making scenarios/backgrounds, but crap at actually making stories out of them so please, feel free to adopt this idea and write/draw something with it. The only thing that I ask is that you please either post it on this subreddit and cite this post, or if it's on AO3, make it a gift to my account on there, Notchbrine.

Thanks for reading this long post lol, please give feedback, whether you liked it or think it needs improvement!