Many people have postulated that it is Shaeonanra speaking through the Mutilated, based on extratextual remarks from the author, as well as hints in the text, such as the speaking in rounds, or the line "the truth spoke with one soul" [paraphrased].

Likewise it has been suggested that the Consult created the Dûnyain, or directed them to Ishual. The biggest difficulty that this theory faces is the fact that the Consult clearly do not know who the Dûnyain are, as seen in the epilogue of TWP, and elsewhere throughout PoN. There are a few way around this, though, and in this post I will present a new explanation for how it could be the Consult do not know who and what the Dûnyain are.

The first explanation is simply that they forgot. We know that you can't raise walls against what is forgotten, and with 3/4 of the Consult leadership being ancient, all it takes is for Shae to become a bit erratic and the whole endeavour falls from memory.
The other possibility is that Shaeonanra set this up in secret, paranoid that his inhuman allies had no need of soul trapping devices, and could choose to deny him the means to keep his soul in the Inward if he displeased them. We only know for certain that Aurang (and possibly Aurax) has no knowledge of the Dûnyain.

These two explanations seem unlikely, though. The problem with the first idea is that the Inchoroi seem to have decent enough memory, so an undertaking such as this would probably not be easily forgotten, and the second falls apart because Shauriatas appears to be on good terms with the rest of the Consult, and they seem to need him as much as he needs them.

My idea is if the Consult has something to do with founding the Dûnyain (far from certain, to say the least) that it was another member of the Mangaecca, not Shae, who set them up. We know that by the First Apocalypse Shae was using his soul trapping larval thing, and that other members of the Mangaecca were able to hold on for an unnatural length of time, but were all dead by round 2. Though Shae might have a privileged position amongst the Consult, there is nothing to say his brothers enjoyed such security.
But if that schoolman should die before his breeding project bore fruit, all knowledge of Ishual would leave the world.

But why is Sil's shield so big? Are you suggesting that the shield is a relic from the days when the Inchoroi were huge, but the Heron Spear is more recent (or was shrunk down from a previously bigger weapon)?
That still doesn't explain how Aurang was able to wrestle the Tall and win.