I was just thinking about some connections in lore from some posts I've read here. I'm not a huge lore buff so I'm not sure how far fetched this is but I would some opinions on it.

Known:
- Sheogorath is the sithis shaped hole left behind when Magnus bailed out on Mundas.
- Sheogorath is/was actually Jggy that was cursed by (supposedly) the other deadra (although his sphere must always exist, they just forced Jggy to become the sphere like what was done to the Leaper Demon and maybe even Malacath)
- Magnus was the 'archetict' of Mundas. He laid down the blue prints if you will. I will take a leap and assume that this takes an ordered mind.
- In the interview with Haskill (kind of official RP that can be found on TIL) he mentions that there are all kinds of things besides Aedra and Deadra. I don't remeber the specific dialogue but is it actually established that Jggy is a deadra whose sphere is order?

Theory:
-Magnus was a spirit (not technically aedra since he didn't actually become part of Mundas) that was probably was very ordered.
- He jumped ship and headed for the hills for whatever reason (most likely didn't want to die to create Mundas) and left a big hole for chaos (now manifested as magic) into Mundas.
- Since this hole is associated with Sheogorath and since Jggy is order aligned could it be possible for Magnus and Jggy to be one and the same or that Jggy is a part of Magnus?

This is just some fun thinking with just a little background into TES lore. Feel free to shoot this theory apart.

Actually, the sun is the hole magnus left when he bailed on mundus. Second is true, Jyg is forced at normal times (although it remains unclear whether jyg and sheo have now been separated) to remain his usual opposite (sheogorath) because of the other princes. Third, si and he IS a god so he must have quite an understanding. If I recall Jyg is indeed a daedra whose sphere is order (he is stasis oddly enough, while usually forced to remain in his opposite, change).

Magnus IS an aedra, though he did not give himself to become part of Mundus like the others did (all the planets are essentially the "corpses" of gods or an incapacity of mortals to see them as they truly are) An aedra is a spirit whose essence is stasis, he simply did not choose to become a spoke of the wheel of Mundus. Im not sure though if the sun is indeed the reason why magic exists in mundus but it certainly facilities the wielding.

I do not recall any instance where sheo is related to the sun or any link between Jyg and Magnus, sorreh :/

Sheogorath is referred to as the "Sithis-shaped hole" of the world in Varieties of Faith, this comes from Aldmeri creation myths and is related to the removal of Lorkhan's divine spark from creation when Trinimac tore out his heart.

Yes my I based myh connection between Sheo and Magnus from Sheo being referred to as the sithis shaped hole.
The way I see it is since Jggy is the deadra of stasis he encompasses both being a aedra and deadra. And since Magnus is in kind of the same boat (being an aedra that didn't actually become part of Mundas) I thought that there be a connection there, especially since Sheo is linked to his exit from Mundas.
Just some wild speculation.
What is the general consenus on who/what Jggy really is and how he fits into things. If he is a deadra then someone or something should have represented his sphere while he was Sheo. As far as I know even if you imprison the specific prince, someone else has to take the role while their imprisoned. Just like when Jggy was released the CoC became Sheo (or someone else took Sheos spot, since it was a PC decision which means lore has to be vague).
So how who was Jggy while Jggy was Sheo?

Ah, well thanks for clearing that up. I remember I had a theory I randomly typed at like 2 am on /r/teslore, may not be linked to magnus, but it does implicate a few iconic people. As far as I know though, Jyg's realm BECOMES Sheo's realm when they switch, literally flipping the table over to see the other side, there can only be one active at a time. As far as I know the two were merged and no one took jyg's place as he left, since he always came back for a time.

"Wait wait wait.. wait... wait wait.. Lets look at the Greymarch for a second here shall we? Cursed to succeed but then fail and return to a chaotic state UNTIL THE CYCLE WAS BROKEN. Lorkhan, according to the loveletter failed on purpose to show everyone else. And as were lead to believe hes done this multiple times as kalpas have gone over and over. Except that this kalpa has been going on for longer than usual, where someone had enough time to actually break the Jyg/sheo cycle. Did I just find out that Lorkhan will succeed or am I randomly speculating?"

It kind of does go with Sheos sphere (mania/dementia) to switch back and forth so it is possible. What is radical dedication to order but a form of madness? But if Jggy was really released how can there still be a sheo? If he's just another personification of the madness sphere why is there also someone else holding the title to prince of madness (the easy answer would be that its just crazy is as crazy does)?
If Jggy isn't part of the madness sphere then what is his connection to Lorkhan (assuming that there is one)?
I remember reading someones post some time ago about how all the TES games keep leading up to Lorkhans release/resurrection, with his Heart being released and the dragon fires extinguishing (forgot how they tied in the mantella and arena's story line).
All this aside, just what does it mean that Sheo is the sithis shaped hole left behind by Magnus? I think that this might mean that the madness sphere was directly created by Magnus's exit, which left a steady stream of sithis leak into Mundas. But this raises another question on the nature of deadra. They didn't participate in the creation of Mundas but they seem to be directly linked to it. They assume spheres based on the spirits/life-forms/peices of aedra that are part of Mundas. Since the sithis leak effected (or affected?) Mundas that constituted the creation of a new sphere. Is this just because they are greedily eating the remains of the aedra and in order to do so assume certain roles related to Mundas to facilitate the collection of souls? That is when a new major aspect of life that is not part of a aedra's influence (something other than love, trade, ect) comes about a new deadric sphere will be created.
Sorry if this make little sense. It's late and I'm just beginning to look into some of TES lore.

Again, though, Sheogorath has no known association with Magnus or the sun; the line you're citing relates him to Lorkhan, not Magnus. Sheogorath is the red rage shaped diamond-fashion where Pelinal Whitestrake's heart should be, singing like a mindless dragon, and the hole in the briast of Al-Esh's spirit, spilling void onto her feet. There's a reason that 3 out of the 4 people who used the Heart of Lorkhan were driven mad by the endeavor.