And that seems like an awfully dangerous method. At least, dangerous above and beyond being in the presence of a Prince with the intent to kill 'em. Suppose that it just gives the Prince even more power?

Of course bad, bad things could certainly occur, but there's no fun in playing it safe.

Do you think it would be possible to use something like the staff of magnus against a Daedric prince? Or some sort of supercharged staff of magnus?

Well, after Jyggalag was released he was no longer a plane of Oblivion? Would he implant himself into another realm and thus become that realm? How can Daedric Princes have more than 1 realm? Or no realms? I think the Prince consciously melds into his realm to make himself more powerful. Not sure, but I don't think the Princes had their realms in the beginning. After all, Meridia was a Magna Ge, and only once expelled form Aetherius did she acquire a realm (unless she pulled a chunk of Aetherius out with her and into Oblivion)

You think you can kill a Daedric prince? Even princes can't call princes. Akatosh couldn't kill Dagon, he had to banish him. Even if you followed that spirt, you couldn't kill it. Umaril was only half Daedra. Well, in a way. He had a Daedric mother or father, not both. He was Ayeild with a smidge of Daedra.The rest was mortal. But that mortal part of him is what allowed him to be killed, and the following of that mortal part of him to Oblivion is what allowed you to wipe him out existence.
As Chaplin puts well, the only thing closest to killing a prince would be for them to forget everything about them self, and enter a deep sleep. Like Cthulhu.
In short, your fighting a uphill battle.

What about if I screwed with the Daedric princes mind, enough for them to willingly forfeit their immortality to become part of the mortal plane, as what happened in the Creation of Nirn. Would that be possible?

Now that the world is created, can additional beings actually contribute to it? I would lean towards no. Once you bake a cake, you can't decide to add aditional ingredients. I suppose that it could expend a portion of its power adding something to the world, but nothing on the level of the Aedra, and not enough to lose its status as a Daedric Prince.

I don't think it's unreasonable to imagine a daedric prince expelling a portion of itself that could then come to "land" on nirn but how would you suitably mind (insent) a daedric prince enough for it to want to do that? considering it has 8 perfect examples as to why it really doesnt want to do that?

On saying that there is the idea that the current daedra would become the next kalpas aedra so i guess it could make sense

I still think that in order to kill a Daedric Prince you'd have to fundamentally remake the Aurbis.

I agree with you there.

Well, then if thats the case, how would Jyggalag stop the other Daedric princes from cursing him again?

Jyggalag's the major monkey wrench in the canon lore. His existence seems to go against so much previous lore. It's a hard one to apologize for.

He was mentioned before Oblivion, let alone SI, but only in a sentence.

SI is great for the casual fans, but it creates a complicated scenario for everyone that wants to fit it in with the story of Sheogorath's creation.

And yet, would you expect the God of Madness's origins to be simple?

To the issue with a gate to Oblivion. In Skyrim we learn that time can be influenced, not only by breaking it but also by manipulation. What is needed is a powerful source with the purpose to do so. As the Elder Scrolls are residues of Creatia, we have strong magical tools that allow us to do with them whatever the hell we want. I think they are even more powerful then the heart of Lorkhan or the Mantella. All "living" things, this includes gods aswell, have to be created through energy. Without energy, there can't be a change. Now the Elder Scrolls are Creatia and Creatia is pure energy. If one knows what to do, I think he can open a gate to any place.

Also, as we have seen, Elder Scrolls are not very hard to obtain. A thief could get one and a Dragonborn aswell.

Then to the bigger issue: I don't really know about the Daedra. Tricking them becoming mortal would be one way to put it, but as they are immortal and far above CHIM, they'll know exactly what you are going for. It's like a chemical reaction. If you want something to happen, you need to invest energy (or a catalyzer) into it or it won't do anything. You have to give a Daedric prince something that is worth loosing his immortality. I doubt that there is anything else. Well, maybe if you promise them Mundus.

Another way could be if you are able to unlink Oblivion from Creatia. Creatia flows through Oblivion to Mundus. Without it, the plane would eventually collaps. The princes are like Towers* on Mundus; they focus the energy but they aren't the main source. If a Lord looses his plane in this way I can imagine that he is very weak. Weak enough to be mortal... still unlikely (here again you could offer him Mundus).

* Maybe they aren't the Towers but the Stones like Alduin was likely to be the Stone to Snowthroat.

I thought the daM s'doG existence was caused by a release of madness when Akatosh slew Lorkhan, creating the Serpent.

For all we know Mehrunes Dagon could've bottled that up and poured the madness into Jyggalag's beer.

This is what i tried to state on another post. Elder's scrolls wikia can't be trusted always. And yes, i readed that Mora holds the knowlodge to kill a Daedra on wikia. Let's not forget, all the mer and men souls are immortal in the afterlife. Well, except on the battle agaisn't Alduin. Anyway you must find a way to cut the Deadra prince link to it's plane, soo his soul will be unable to scape. If an Aedra can die, because they are on Mundus. Aka: their plane. Probaly Daedra can die, but only on their plane.

I'm not sure, but wouldn't binding a Daedra to Ebony armor "kill" them?

No. It just makes it really hard for them to return.

Daedric Princes have to be killable, or else a fight between them would be unlogical.

I doubt they fight each other to death but more to gain more influence on whatever plane they fight about. Molag Bal wanted us to kill the servant of Boethia. I assume it was to decrease Boethias power and increase it's own.

Probaly. Also about Jyggalag. How did he achived that much powers? He could just help mortals alot or love them, and they would love him and worship him. Increasing his powers to insane stats.

If they appear on Nirn they can be beaten... This has happened several times in the past.
In their realms they probably can't be killed, but that doesn't mean that somebody can't make them weaker and himself stronger in the process.