I am in the middle of writing a quest mod for Skyrim, and I would like for some information to be obtained by the player, in a book of such from Apocrypha.

It is said that the knowledge to kill a Daedra exists in Hermaeus Mora's plane of Oblivion. Given that, what would be the most likely or more specifically the most likely lore friendly way of killing a Daedra?

A book on the matter: http://www.imperial-library.info/content/spirit-daedra.

so upon reading this, it appears as though if you kill the body the spirit remains and returns to the plane of oblivion. This reminds me of the Knights of the Nine quest, where you follow Umaril the Unfeathered, into Meridia's plane of oblivion. Perhaps something similar can happen with the Daedric Princes? To defeat the Daedric Prince one would need to sever the bodies connection to their plane of oblivion and kill their body, what of the Animus then?

Considering the Daedric Princes are their planes, I don't think you'd have much luck.

so then the question would boil down to how to annihilate a plane of oblivion and thus kill the Daedric prince. I am not too versed in this part of the lore. but there does exist a number of planes of oblivion that are not under the ownership of any Daedric prince, how did these come into existence? Could there be a way of simply turning the daedric prince completely and irreversibly into an oblivion plane, with no way of undoing this? or is there some other way?

Umaril wasn't a daedra, and shouldn't be used as an example of how they operate. He was a mortal demigod who sold his soul to Meridia, and as such could be killed (albeit, with some difficulty.) If you replace Meridia with Azura, I don't think the comparison to an Ayleid version of Nerevar would be out of line.

yes of course, I was simply referring to how the book was explaining how to kill a normal daedra, not a daedric prince, where if only the body was killed its spirit would make its way back to oblivion for it to be made again. I simply extended the argument saying that if you somehow stopped the spirit of the dead daedra from returning to oblivion that you would in affect kill the daedra. Does this make sense? or have my assumptions been wrongly placed?

Given the relationship between a Prince and it's plane, no, that wouldn't work.

Shehai splitting of the atomos everywhere in a realm. Hmm....

Scrambling the animus of a lesser Daedroth doesn't seem like a huge issue on the surface, but if that Daedroth is the product of a Prince's realm, you're dealing with Princes again. Basically it boils down to destroying energy instead of diverting, trapping, or changing it. A lofty task.

Ok, lets say that I had the power of a Daedric Prince to use, specifically Jyggalag?

The other Daedra couldn't even kill Jyggalag; they had to curse him.

Or to use Chaplain's terminology, they changed his nature. Nothing destroyed, nothing created, but a heck of a lot changed.

I just read up on this a bit, and it seems like something that could do it.

The story goes, Jyggalag bent on retribution searches for the knowledge to kill a daedric prince, which as lore states is kept in Apocrypha. If the knowledge about how to kill a daedric prince,is the use of some massive Shehai "explosion" caused by some event inside the plane of oblivion of some daedric prince, would that be enough to kill the Daedrc prince? And for argument sake you could channel the direct power of Magnus into this event?

source?

hmm, I am having trouble with finding the source of the rumor,

but apparently in Daggerfall there was a rumor that said that the hidden knowledge for killing a Daedra is contained within Apocrypha the plane of oblivion of hermaeus Mora. But I cant confirm this, I dont know where to get a list of rumors from Daggerfall, or whether even if I got the list, whether this would count as a legitimate source of knowledge. I'm not sure

One can find everything in Hermaus Mora's realm, except what one is looking for.

hmm, what if the person searching was tricked in a way that he finds what someone else was searching for, not what he was searching for? Could it be possible?

If it's not what you're looking for, chances are you will discard it. If you find yourself looking in Apocrypha for something, I'll bet that you are a really desperate man and likely to not care for any rare pieces of information you will find.

"No, I don't want to kill a Daedric Prince, I want to know how I can get into the Chapel of Dibella without actually being in there!" *chucks book*

This is the Aurbis we're in. Whatever can't be killed through normal means can be killed through mythic means. The Daedra may seem very powerful, but they're mostly seen from the perspective of mortals who can't hope to match their power. If you take a step away from Mundus though, you're looking at an egg. Who's to say if energy can't be destroyed here. Who's to say you even need to destroy energy to kill a Daedroth? If you take away a man's memories to the point where he no longer acts like he usually would, you have destroyed what makes him him. I'd wager the same could be done with a Daedroth. Focus Aurbic energy through itself. Pierce Aetherius. Focus until the Tower appears. Dance on it. Start changing things. Play a shell game with the Daedroth's bits and pieces until not even the Prince can keep up with the movements of his own mind. Make him forget what he is. Force him to wake up, and laugh as a Plane reaches Zero-Sum or tucks itself so deeply into sleep, that the Prince forgets he is his realm, and the realm itself settles into a calm landscape; a sleeping god forever unaware of itself.

That's one way to do it. I was thinking that causing enough nuclear explosions in a plane(t) could weaken a Daedroth's soul to the point of being capturable/manipulable. Then you grab the soul and force it through the Dreamsleeve. Yikes.

Hmm, I am yet to read them yet, but the Infernal City books, dont they talk about separating a bit of Clavicus Vile's Oblivion plane? Could something similar to that be used on such a scale as to rip the oblivion plane apart completely? Thats it right, if you destroy the oblivion plane you destroy the Daedric prince?

So, you move a portion of a prince to another location? Makes no sense. Also, it was CV separating himself, as he was also Umbra, though much more rogue. Same deal with Barbaras from what it seems in Skyrim.

In short, no. Also in order to really kill the prince, the concept they embody would have to be stricken from perspective.

Ok, so eventually what I would like is some sort of method or technique that Jyggalag could use to prevent the other Daedric Princes from coming together and cursing him again. I believe that he would want to make sure everything stays as it is in its natural order, and for that to happen he needs to prevent them from cursing him again. To make the other Daedric Princes forthcoming, he threatens them with mortality of some sort, this threat prevents them from acting again. I was hoping that this threat could be the hidden knowledge of how to kill a Daedra, but more likely it seems to be that instead changing the very aspect of the Daedra in question is more plausible as it has happened before. But I want to make it more permanent.

You must get a massive black soul gem and then you cast soul trap on the Daedric prince. When you fight it, make sure you're lvl 50+ and are using endgame gear, probably dual enchanted legendary daedric or dragon armor. When you trap the soul, go to an enchanting altar and enchant either a pickaxe or a woodcutting axe. Bury the pickaxe or woodaxe in the bottom of a dungeon and the daedric prince will never be seen again.