This information is based on alternate scenes or materials, and is not considered canon within the overall plot of the AU.
(Note, this is not at all a canon thing I found from comics or other sources. I just figured that it's slightly idiotic that this page was just an absolutely carbon copy of Error's, but with name swaps.)
Error!Swap Papyrus is an AU destroyer. In this AU, he is bent on destroying all AUs and things he considers 'glitches' or 'mistakes' in the multiverse. He uses orange strings to tie up and shatter souls, and if the strings go inside a victim, he will be able to transfer his soul into the victim, making his body turn to nothing but turning the victim into him, controlling them to do whatever he likes and leaving the victim helpless. He can jump from one universe to another, as well as having several other glitchy powers/quirks. His AU connects to many others, so it's best to get to know some other AUs before you jump into this one.
ErrorSwap Papyrus basically is an AU hunter. Rather than Canon Error, who seeks to destroy all AUs himself. ErrorSwap would rather only deal with more difficult ones himself; manipulating his underlings into doing most of the dirty work for him. ErrorSwap tries to avoid detection from entities such as Ink!Sans or X-Gaster, due to them being a threat to his operations. He knows about Error, but he just doesn't care about him.
Chara does a Genocide route over and over; to the point Papyrus goes insane and kills all his friends in a DustSwap esc. Event. Eventually, he defies the timeline and kills Chara. This causes a massive glitch, which causes what remains of the timeline to be eradicated, other than Papyrus himself. He turns into an Error. He's left in the void for thousands of years, until he goes insane and loses basically all memory of his past life. Ink enters his AU, due to the strange nature of it. Papyrus, learning about alternate universes existence, decides to flee through the portal Ink made. He does this via teleportation, going unnoticed by Ink. He then analyzes The Doodle Sphere, giving him the knowledge of how to AU jump.
He has been stated to be a complete mystery due to the erratic and unpredictable behaviors he has. He keeps puppet versions of his other selves that he talks to, calling standard Papyrus “Papyrus classic” and naming the other ones by numbers. Swapfell is “Papyrus abomination number 13″. He refuses to discuss Sans. At all. Despite admitting he is a glitch/anomaly, he is different since he’s the only one doing something about it. He really wants to hunt down CORE!Frisk/CORE!Chara.
ErrorSwap has Nyctophobia (the fear of the dark), and is therefore very easy to scare. He doesn't like any AUs that are extremely dark, either. Such as Underworld.
At random intervals he can glitch up, filling his eye sockets with errors, giving him a major disadvantage if he's in battle. If ErrorSwap Papyrus had no strings, he would be a very easy problem to fix.
ErrorSwap is blind in his left eye. He keeps a human eye in there, the code of which he manipulated to allow him to see out of that eye. However, it can be hit. If you do, it'll blind him partially again and cause him great pain. It's mostly his weak point.
He is also supposedly weak to water, but no one knows for sure yet
They get along, somehow. He seemingly seems to not care about destroying Undertale, simply because of the fact he doesn't care. It's not that he sees Undertale as perfect; he just seems to like it. Therefore, he likes Classic Papyrus. He kidnapped him, but released him due to being impressed at how determined Sans was to defeat him. So he gave him Papyrus back as a "Pity gift."
He was the first AU Inkswap encountered. InkSwap had his suspicions that other beings existed, but not entire universes. ErrorSwap talked about AUs and how terrible they were. Inkswap was suspicious of him, due to how clearly insane he was. InkSwap doesn't trust ErrorSwap that much, however they are somewhat friends. InkSwap has never mentioned his brother to Errorswap, due to his lack of trust for him.
He thinks that CORE Frisk is disgusting, but other than that, he couldn't care less about them. He described them as "THEY'RE THE SHORTER SKELETON'S PREY; NOT MINE." To InkSwap Papyrus.
ErrorSwap hates Freshswap completely. Between him and Error; this remains the same.
Some people ship them. However the ship is not, and never will be canon. Errorswap has tried to have Freshswap killed multiple times. Eventually, he was able to trap Freshswap into a void of code, where he believed Freshswap was destroyed/trapped. He has mostly forgot about Freshswap since.
He knows about Fresh, and avoids him at all costs. Knowing how hard it is to kill someone like him, he decides it's best he just never gets Fresh's attention. He never tried to kill him, unlike Fresh's swapped counterpart.
Papyrus believes the only other Error that exists is Errortale!Sans, however a brother of his exists in the glitches of the multiverse. He is mostly apathetic towards Error, however he seems to generally dislike discussing Underswap Sans. So it's quite likely that he'd care more for Sans if he knew about him.
Error once destroyed a timeline called Alphaswap which was the first ever version of Underswap and its Swap AU's ever, but unknown to this day everyone that has ever existed in the Underswap AU's never heard of Alphaswap ever.
Error mostly created a dark version of Underswap from the resetted files called Happyswap which isn't really happy at all. ErrorSwap, in order to fix this, kidnapped Dream, and manipulated him into stuffing it full of positivity. Everyone in the AU is happy, however no one other than Papyrus and Dream knows why, due to how the AU is. Dream doesn't know who kidnapped him, due to Papyrus altering his voice via glitches to sound like a Sans. Due to the surplus of Sanses, Dream has no idea who it was. Due to the glitches he thought he heard, he thinks it was Error!Sans.