What is Auxiliary?

[Yumiya]

There are a number of theories floating around about who/what Aux is. We know a couple of things for sure:

• Auxiliary claims to be dead
• Auxiliary is referred to as a spren
• Auxiliary acts as a living shardblade by changing shape
• Auxiliary is probably not a bonded cognitive shadow of a dead knight radiant (WOB)
• Auxiliary refers to himself as knight and Nomad as a squire
• Auxiliary can absorb and then use multiple types of investiture 
• Auxiliary can manipulate spirit webs with what looks like Spiritual Adhesion 
• Auxiliary can initiate a Skip to transport Sigzil, assuming he has enough investiture

Before I really get started, there is a WOB that is brought up frequently in these discussions:

 

Quote

AdelRD

Should we assume that Sigzil’s Dawnshard is the same that Hoid used to have?

Brandon Sanderson

Sigzil, at one point, held the same Dawnshard that Hoid used to have. I phrased that very intentionally.

Secret Project #4 Reveal and Livestream (March 29, 2022)

I think the intentionality refers to the clause "at one point", as in Sigzil held the dawnshard prior to this book but after SA4. And there is no additional implication. We know that Sigzil no longer has the Dawnshard: " An after-effect of the burden he’d once carried, the thing that had given him his Torment." This is important, because it means that all the abilities Aux shows are innate as are Sigzil's.

As a couple of other posts have deduced, Bondsmith surges seem very similar to Aux's abilities. Spiritual Adhesion to allow Connection between Nomad and the planet and between Nomad and Hoid. Aux can also fuel Skipping, which seems similar to how Dalinar summons perpendicularity, though Brandon did confirm that skipping doesn't require the use of a perpendicularity.

So, I propose that sometime before SP4, a new Bondsmith was added to the order. We are led to believe it is possible in Words of Radiance, in Epigraph 44.
 

Quote

"But as for the Bondsmiths, they had members only three, which number was not uncommon for them; nor did they seek to increase this by great bounds, for during the times of Madasa, only one of their order was in continual accompaniment of Urithiru and its thrones. Their spren was understood to be specific, and to persuade them to grow to the magnitude of the other orders was seen as seditious."

 The name itself is most reminiscent of the unique spren that Bondsmiths bond. Auxiliary as in "a person or thing providing supplementary or additional help and support." Makes sense that if a new bondsmith was created, that it would because help was needed.  Even Sibling was created with the specific purpose to oppose Odium. Why not a 4th in the most desperate times? Not sure who would bond Aux but maybe someone we have not met.

Now, Auxiliary claims to be dead. When a radiant abandons the oaths, the spren turns deadeye, and deadeyes are not vocal like Aux. So what happened? There is a WOB that might shed a little light. 
 

Quote

Brandon Sanderson

Yeah, they actually mix. When the bonding is happening, what's happening is that the gaps in the souls are being filled with the spren's <essence>. And they are actually melding into one 

Brandon Sanderson

And they are actually melding into one individual *inaudible*.

yulerule

<And the minds are separate?>

Brandon Sanderson

Yeah, mhm.

Arcanum Unbounded Hoboken signing (Dec. 3, 2016)

So, what happens to a spren that has completely melded into one with their radiant if that radiant dies or forswears? Could the mind of the radiant persist as a sub personality of the spren while the spren gains the ability to manifest without an additional bond (given that they are still basically bonded to the dead knight)? The knight's mind and the spren's body. If this is true, it would explain the odd third person dialog from Aux. It would also explain why he refers to himself as a knight.

But why is Nomad a squire? He was a knight radiant last we heard, a windrunner. We do know that Bondmiths have squires:
 

Quote

Even though there can only be three full members, there were times that some Bondsmiths did take squires. Beyond that, many of the retinues that protected the Bondsmiths were considered members of the Order–going so far as to swear oaths, even though they didn’t have a spren and never would. Some even called this the most pure form of being a Radiant, because these were oaths sworn not in the name of gaining powers, but simply for the good of the oaths themselves.

Well, maybe Sigzil, being apart of the Bondsmith's retinue qualified him to being both a squire and a knight, at least in Aux's mind. Now, what about Nomad's lack of oaths, oaths ended and forgotten. Oath's that were suppose to override part of the Torment. 

Lets say that Wit convinces or tricks  Sigzil into picking up the Dawnshard while still bonded to his Honor spren. We know that it could cause problems and that something did/is happening with his spren because of the Dawnshard
 

Quote

AdelRD

Whatever is happening to Sigzil and his spren, is it related to the fact that the Sleepless forbid Rysn to bond a spren?

Brandon Sanderson

Yes. Also a good question.

Brandon Sanderson

Let's just say you are finding out, or Sigzil is finding out first hand part of why that warning was in place. And he didn't get that warning. He should have. Let's say that other people in the Cosmere have been able to do it without it being a problem. And so, you know, if you happen to be an age-old immortal master of multiple arcanum, then you can get away with things that poor people like Sigzil have more trouble with.

Secret Project #4 Reveal and Livestream (March 29, 2022)

So we know that having a bond with a spren means that their essence is filling in cracks in the spirit web. Holding a Dawnshard does the same thing. What happens when those two forces start overfilling the cracks or even worse, fighting over the space. I cannot imagine anything good for the Radiant or the spren. So Sigzil and his spren mutually decide to end the bond. But, that time while being bonded and holding the Dawnshard has greatly increased his Torment. 

So, now lacking a blade of his own, Sigzil and Aux (now the semi-deadeye) teamup and the resonance between Aux's surges and Sigzil's investment from being a Dawnshard for a time, allow for skipping.  

[S. Stormy]

Oh wow! That... makes a lot of sense! That... sounds incredibly plausible and likely. 

But seriously! Good job! Finally a theory that I have enough Cosmere knowledge to understand! I wish I could upvote it more than once.