I never shared it, but I made a fic a long time ago about someone taking Mangle home and fixing them up. It was more along the lines of Mangle being haunted, and I can't remember the details (I'd have to find the fic somewhere on my computer lol), but I do remember it being wholesome, and Mangle does thank the person who bought them to fix them up, but vanishes.
It made me think about the yandere Lolbit AU. In this AU, obviously, Lolbit isn't haunted. While I haven't been able to do anything with this AU (not enough time/can't animate), I really like it. In that AU, Lolbit is a yandere because she gets attached to a technician (still have yet to decide if it's Michael or not lol) after being stuck in a room for so long. Specifically, a room where she handles software security, coding, and other things. She's a physical animatronic, but I did expand on that a bit in the sense that she can insert her own software into computer software and return to her body. I might be able to expand on this as well. Think of her as being a sentient antivirus in this state, but also an AI who has full control over the OS in that moment.
As for Mangle, I came up with some yandere Mangle ideas. Foxy works too. I swear, it's a coincidence that I keep choosing foxes for this! I have some yandere ideas for non-haunted Mangle and Foxy.
Basically, in these AUs, both want to be fixed. Both are neglected. Mangle has the advantage of still being loved by kids, but Foxy is forced not to interact with them (even worse for Withered Foxy, if he's chosen for this). Either way, both are damaged.
For Foxy's AU, it'd involve the nightguard. The nightguard in this scenario would merely give him some positive attention, peeking behind the curtains, maybe remarking that he deserves more love or something. After this, Foxy goes nuts for the nightguard. Since the animatronics aren't haunted in this AU, I have to decide why they'd attack the nightguard. I've had AUs where I've done this before. Anyway, he viciously attacks the others if they continue to try to harm the nightguard. He, in all his pirate glory, wishes to "hoard his treasure." His treasure is the nightguard in this case. I feel like he'd definitely successfully kidnap them. I don't think he'd let them leave after the night is over the way Lolbit might, but she has the advantage of being let out unintentionally or even hacking software.
With Mangle, this can go one of two ways (technically three, which I will explain later): Similarly, the nightguard shows Mangle some sympathy and attention while she's in her off state. I decided to make her a female in this AU because I usually do, because this is a free universe, and because the fandom likes that. Anyway. After this, Mangle protects the nightguard, perhaps more viciously than Foxy, mainly because she can swing from above without being detected by the others and cause serious damage. There's also the technician route, where she could get all fixed up by a technician and become obsessed with them. She wouldn't have the advantage of swinging from the ceiling, but she'd still have tricks up her sleeve if the other animatronics pursued the technician, although this is less likely to happen since they aren't the nightguard in this case. Though an animatronic did attack an adult, possibly an employee, in FNAF 2, who wasn't a nightguard, which could happen; in which case, Mangle would simply "deal with them." I can see yandere Mangle being an absolute menace. Instead of being called "The Mangle" because she's mangled, she'd be called that because she'd be mangling others at that point lol.
There's an alternate technician route, based on my fanfic, where someone could take her home to repair her. They could either just be an enthusiast who wishes to keep her and fix her for themselves and buy them the way they do in the fic I made, or they could be an actual technician hired to fix her up.
I love the yandere trope (obviously), and these guys are fun to explore it with! Ballora, CTW Funtime Freddy, the SOTM girls, maybe even Roxy would suit this trope as well? If I could make an AU where the AR skins would make sense, Black Heart Bonnie and Heartsick Baby would also work.