Theory: Eclipse was created as a patch for Sun and Moon after they were Daycare Attendants, and they were successfully rebooted once before!
I often think about Ruin. I think about how Sun looked at the Faz-Wrench when Cassie walked in with it and immediately knew that he could be rebooted with it. I always wondered how he knew that, and I also wondered how in the world he hadn't been rebooted before if it were that simple, and if he could have told a technician to use it on him in the past.
My first theory is that he did tell them and they didn't listen to him, but that one is weird. This theory stems from the obvious neglect he has, and that he is salty that he wasn't programmed to be able to fix things like the carousel breaking down. We know that animatronics are capable of reporting to higher-ups. Freddy himself does this about something that concerns him. Maybe he tried sending in reports and talking to human technicians when they existed, but they disregarded it or were told by a mysterious person (probably Vanessa/Vanny) to disregard anything poor Sun said. But that did feel unlikely. I feel like the staff tried all that they could.
My next theory was that Sun knew from the past. He is an old animatronic. Sun/Moon/Eclipse was probably refurbished, and this is likely not what he originally looked like. Their programming was changed from a theatre bot to a daycare attendant.
In the games, it was implied that Moon started acting out after he had already been switched over to be a daycare attendant. It was implied that he was once a great animatronic in the daycare, and that he took part in the daycare at all to begin with, whereas one of the books implied that they decided to shove Sun into the daycare hastily as the daycare attendant and then use the generators to keep the lights on because he was acting out when he was still a theatre animatronic. The game logic makes more sense to me, personally. I think he was a theatre attendant, but he was transferred at one point.
I wondered if it was because Eclipse stopped working. Eclipse was there for a reason, right? But what confuses me is that Eclipse acts like a daycare attendant when we reboot him. A daycare attendant with daycare protocols. He doesn't act like a theatre animatronic programmed to be part of the show.
So that's where I tossed both theories out the window and came up with a new one: Eclipse was created after. By a technician who used the Faz-Wrench rather than an older Data-Diver or variant of it. He was indeed created within the Pizzaplex.
This, perhaps, means that Eclipse was created while Sun and Moon were daycare attendants. He was created to merge them, to provide them with stability. When rebooted, they became him.
I should add that Moon didn't want to be rebooted. Both Sun and Moon knew the outcome of being rebooted.
This makes sense. They simply "couldn't be fixed," according to the books. But if someone had tried, this would have been the fix.
So...then what happened? Why were they never rebooted again?
Of course, Moon's glitchy, sadistic behaviour is Vanny's doing. She wouldn't want a fix! That was her intention all along. So, what did she do? She reset Eclipse back to Sun and Moon, leaving Fazbear Entertainment and whoever fixed them to believe that it wasn't a successful fix. She could have possibly killed whoever fixed them as well, ensuring that nobody else knew about the fix.
But Sun and Moon would remember. It's clear she didn't mess with their memories as she did with the Glamrocks. Sun would remember. Moon would as well. Sun would no longer have anyone to tell, obviously, once staff bots replaced the human technicians. Especially because they were under Vanny's control. Even if he did, there would need to be an available Faz-Wrench.
Eclipse seems to be intentionally made to provide stability to a daycare attendant, not a theatre bot. Even in SOTM, we see signs of Sun and Moon existing, not a merge of the two. There is nothing to imply that Edwin created anything Eclipse-related. Whenever the animatronic itself was first made, it would have been to perform. Eclipse's protocols were daycare-related. It makes sense when you remember that the company had an incentive to fix Moon, as they had complaints flooding in about him terrorizing their children out of the blue.
So...yeah. I really think Eclipse was a patch made after Moon started acting out, by a technician who attempted to fix the pressing issue of a malfunctioning daycare attendant, especially when you take into consideration that Moon was indeed a daycare attendant who did function normally at some point if you look at the context of the games only. Eclipse really does feel like a merge of the two in that context. Then, Vanny realized this and simply reset them, making it look like a failure and possibly killing the technician who repaired them so that they wouldn't return, and Sun had nobody to tell anyway.
So yeah. That's my theory. I used to think that Eclipse existed before. But I don't think so now. I think he is a patch, and I think that Sun and Moon were rebooted into him very briefly, only for Vanny to put a stop to it, and for him to have nobody to tell once Vanessa was the last human worker.
Edit: I guess I should add that SOTM is weird about Sun and Moon. We have that weird thing in Moon.exe with the Moon statue, but I don't think Eclipse is relevant to that. That seems to be more in relation to Edwin Murray allegories, though the statue resembles Moon a lot. There is nothing to indicate that Sun and Moon ever really started off as anything other than that: Sun and Moon. The player/Arnold also does not build Sun and Moon's animatronic form, though the game could possibly allude to aspects of their creation that we have yet to see. I do not think Eclipse existed in the past.
I do hope Eclipse's existence is touched upon. Sun wanted to reboot and become him, and Moon did not want to. Both knew that Eclipse existed. We know nothing about him.
So, yeah, my theory is that Eclipse is a patch meant to stabilize the two, and I simply hope that we see more of him!