Im im going through my 4th re-read and been making up crackpot theories as I go. And one thing that stood out to me was that we know so very little about Dai-Gonarthis. No one seems to know what his influence on Roshar is other than he may have had a hand in the Scouring of Aimia.

My theory is that Dai-Gonarthis has the ability to allow people to hear the dead. This or convinces people that they are hearing the dead.

There are multiple mentions of characters within the world hearing the screams of the dead, specificly the dead they killed. Most notable are probably Szeth and Dalinar. I feel like this is brushed off as them both having some form of PTSD and regret for their killings but I don't think that's all it is. It seems too vivid. To common and mentioned far too often.

It would also align with the other powers of the unmade, similar to the death rattles and the thrill having an effect on senses and emotions of the inhabitants of Roshar.

Lastly, the death Rattle mentioning The Black Fisher: "Let me no longer hurt! Let me no longer weep! Dai-gonarthis! The Black Fisher holds my sorrow and consumes it!"

Perhaps on death the unmade consumes the dyings pain and suffering to then present them in the minds of others? Perhaps Dai-Gonarthis and Moelach are lumped together because they both use the dying to further their effects and that's why there is only 8 understood Unmade?

I could be way off but I just wanted to write this down to point it out if it ever is proven.