Thought about what @silvercrow72 said to me during this one scene in TPOT 23 for a measly five minutes before coming up with my own half-assed theory
This post is going to be half me sharing my thoughts on what could have caused the negative outbreak, half me trying to infect you with my zombie Four headcanon.
...Get it? Infect- hey hey HEY WAIT COME BAC-
It's unclear what year it is when Zro and Fifteen discovered the yoylite, but I'm going to assume this happened the same night One figured out the power of the yoylite, or at least around that time. To me, it looks like the chunk of yoylite that transformed Seventeen into a negative zombie is the same chunk that One kicked off the cliff in TPOT 20. I don't have any reason to believe that it's a separate piece of yoylite that fell from the sky.
In my mind, either one of two things could've happened.
Seventeen got bonked on the head by the falling yoylite chunk hard enough for it to have done something weird. Yes, as silly as it sounds, this is a genuine possibility in my mind. I don't recall a piece of yoylite falling really hard on any other algebralien's head in the show. And I don't think that one scene where One made a piece of yoylite float above her head and then lost focus counted, because it was just a few feet above her, which seems like nothing compared to the height of the cliff.
Seventeen was messing around with the yoylite and ended trying something similar to One's method of extracting power from it, but something went wrong during the power transfer. So instead of Seventeen absorbing the yoylite's power, the yoylite absorbed Seventeen's soul. (or something like that)
I'm more tempted to believe the second outcome, because the first one's logic wouldn't apply to my zombie Four theory. For the rest of the post, the first outcome will be ignored.
I took a close look at what little we've seen of the negatives so far. One of the zeroes said, "they don't seem to have any will or purpose". I think that whatever is left in those shells does has at least one goal - to turn more people into negatives. But when they're not zombie zapping other algebraliens, they're either standing like idle video game characters, or moving in quick bursts of motion. The way negative Fifty Five moved during one scene was hyper and twitchy.
In the scene where we first see normal Fifty Five and negative Seventeen, I don't know what the hell Seventeen is supposed to be doing with her arms, but it almost looks like they're feeling around their own face, trying to figure out what's going on themself. They might have still been in there for a few seconds before losing themself to the yoylite's effects. Yeah, the arm movements could just be normal zombie behaviour, but like I pointed out, the movement of negative Fifty Five didn't look so slow.
I also think these guys won't just throw zombie zaps when there's a target. They seem to do it randomly and in whatever direction. Negative Fifty Five literally shot a beam into the sky where there shouldn't be anyone to zombify.
I know these details don't seem to be going anywhere. I just felt like analyzing what we know about this apocalypse that feels like such a big thing but at the same time feels like it's never gonna be touched on in the series again ;v;
Now time to do what I do best and that is RAMBLE ABOUT FOUR oh come on don't leave now you knew this was coming- Silver connecting this algebralien zombie thing to Four is what got me interested in the first place come on please stay-
Alright I think my theory has already gone to shit because I have nothing solid to stand on here and I might even get some stuff wrong, but still just let me yap. First off, like Silver said, the way the negatives' eyes black out when zombified is very similar if not the same as how Four's eyes turn black when he gets really mad. Just from this, I started thinking that maybe some of Four's violence comes from him being part zombie.
Yeah, he was already a bit violent in TPOT 20 which was shown by him throwing a ball at Five with way more force than necessary, but I think him being part zombie contributes to how it gets so much worse eventually.
I think like with Seventeen, something went wrong when Four tried to transfer all the power from the yoylite meteor to himself. Maybe it was a simple mistake or maybe it was stress. One of two things could have happened.
Four simply didn't transfer the power properly and partial zombie-like behavior was a side effect.
Four was turned entirely into a negative, and with X's help, Four was fixed before One showed up, but not entirely fixed because X didn't know what he was doing.
Since the piece of yoylite that affected Seventeen still had its colour, I think X may have ended up being the one extracting the power from the yoylite meteor, and then used that power to fix Four, but not properly. Four not immediately having his mind taken over by this zombie state could have given X more time to do something. Then X would give half of that power to Four, if we're still going with the theory that Four and X each have an equal share of the meteor's power. X could have fixed Four with the little power he had already and just let Four take the power from the meteor too, but I can't really imagine it.
We've seen Four use his zappies a lot over the course of BFB and TPOT. I don't think that's just another ability. We also see that the negatives turn other normal algebraliens into negatives using some kind of zap. Four using it so often might come from some kind of zombie urge to infect others. Other algebraliens don't use it as much, but to them, it IS just another ability, because nothing in their brain is telling them to zap others.
I know that there's multiple causes behind his violence in BFB. He already seems to not have cared too much about hurting some others he doesn't particularly care about in TPOT 20. Then there's BFDI. From what Four has seen on the TV and from the objects surrounding him and X on Earth, death isn't a big deal to them. It's something they easily come back from and often don't even seem to care about. But I don't that Four would have actually tried to kill someone if he was normal. There is still the trauma from Three. He definitely wouldn't want anything bad happening to X. If anything did happen to X, Four would have to use his own power to recover X and risk him ending up like Three because of the lack of an algebralien recovery center. I don't think Four would want to end a life just to test if he can properly recover others.
Now here's the crazy story I have in mind.
What if X did something that made Four really mad, and when it got too much, he stopped repressing the urge to infect and sent a zap X's way that killed him? Then Four would have no choice but to attempt to recover X, and that's how he would learn recovery, otherwise he may have never risked trying to learn how to recover people. Yeah, X could have died in some other way that would force Four to have to learn recovery, but let me play with my silly little delusions for a bit.