What the Fuck Happened to Jyggalag: A History of the Prince of Order
Stern Jyggalag
sets order on its path
~Skald Skullsplitter in Darkest Divinities
Before some clown decided to start recording history, Jyggalag ruled over a realm of perfect order across the seas of Oblivion, aided by his librarian and later overall-chamberlain Dyus of Mytheria. This realm of perfect order and intense power Jyggalag held was generally considered a bad thing among the other Daedric Princes. They made him turn into Sheogorath and his realm into the Shivering Isles, but at the end of every Era he would turn back into Jyggalag and retake the Shivering Isles. At the end of this Greymarch, he turned back into Sheogorath, starting the cycle over again.
In 3E 433 (during the Shivering Isles DLC of Oblivion), someone popped open a doorway to the Shivering Isles in Niben Bay. Someone (the Champion of Cyrodiil) got the idea to go check on that. Sheogorath called dibs on them and made them his new mortal Champion because he could tell a new Greymarch was about to begin because Knights of Order (soulless servitors of Jyggalag) appeared in the Isles and weird obelisks started popping up. As it turns out, Sheogorath had a new and fun idea to break the cycle that Sheogorath-Jyggalag had been trapped in - the Champion would mantle the powers of Sheogorath, in the hopes that it would free Jyggalag to just be himself.
This would ultimately be true - the new Sheogorath would take the throne and Jyggalag would have his forces attack Sheogorath's Palace, ultimately culminating in an anime-esque duel between the two where the Champion would fight until Jyggalag yielded and congratulated the Champion on breaking the cycle.
Jyggalag then fucked off into Oblivion somewhere for reasons unknown. His ever-exhausted librarian Dyus figured that he would either be seeking revenge or pursue loftier goals, even potentially never returning to the Shivering Isles.
Strangely, some time in the Fourth Era, Sheogorath was said to have been driven even more mad by his memories of being Jyggalag, implying that either the Shivering Isles DLC didn't happen in the overall lore, or that mantling a role also included getting all the memories. Talym Rend, a Dunmer, was able to defeat Sheogorath at his own madness game by making the Madgod relive these memories.
And then we get to the events of Skyrim in 4E 201, when the mage Thoron got the Sword of Jyggalag and started a ritual to tear the veil between Tamriel and the Shivering Isles to ultimately destroy the Isles in a manner similar to the Greymarches. The Last Dragonborn put an end to the ritual by killing Thoron and taking the sword themself.
Overall, it's warned that Jyggalag will one day reassume his role with unknown ramifications for the complicated balance of power within Oblivion.
As mentioned in the Thoron paragraph, Jyggalag has just one Daedric Artifact - the Sword of Jyggalag. It was also said that replicas of the sword have been in existence since around 2E 582. His sword has been all over the place - the throne room of Sheogorath's Palace after he yielded to the Champion/New Sheogorath, in Talym Rend's possession before he decided to cause problems on purpose, in the possession of the mage Thoron before he got bodied by the Last Dragonborn, and possibly even in the possession of the Golden Saint Staada. It's a giant fuck-you claymore that's perfectly symmetrical and made of a weird silver crystalline material. It has an enchantment that allows those that gaze upon its edge to see the past, present, and future flow as one.
Because Jyggalag is overall less-covered than every other Daedric Prince and intrinsically tied to Sheogorath, TES pagans and witches have had to build things from the ground up to figure out how and what to use to worship Jyggalag.
Altar ideas, offerings, and symbols can include:
books (especially nonfiction, scientific research)
crystals in geometric shapes
planets (Earth, Jupiter, Mercury, Pluto, Saturn)
traditional kinds of incense
white flowers (and wreaths including them)
Devotional activities can include:
linear ritual/spell working
participating in activism
putting things in order for future events
reflecting on past events
Summoning days may include:
28 Sun's Dusk (November 28th)
31 Evening Star (December 31st)
Jyggalag's lore page on the Unofficial Elder Scrolls Pages: https://en.uesp.net/wiki/Lore:Jyggalag
Jyggalag's page on the Elder Scrolls Wiki: https://elderscrolls.fandom.com/wiki/Jyggalag
"Darkest Divinities" by Skald Skullsplitter on the Unofficial Elder Scrolls Pages: https://en.uesp.net/wiki/Lore:Darkest_Divinities
"Jyggalag - Daedric Prince of Logical Order" by @wickedenbywitch-moved on Tumblr: https://the-college-of-whispers.tumblr.com/post/668609374379507712/the-lore-jyggalag-is-the-daedric-prince-of
@shadow-path on Tumblr on what Jyggalag's summoning day may be: https://the-college-of-whispers.tumblr.com/post/661517412085219328/shadow-path-i-cant-help-but-wonder-what
"Altar Ideas/Offerings for Daedric Princes" by @shadowedpath on Tumblr: https://the-college-of-whispers.tumblr.com/post/661506022668697601/altar-ideasofferings-for-daedric-princes
"Astronomy" by @the-college-of-whispers on Tumblr: https://the-college-of-whispers.tumblr.com/post/663310441320153088/astronomy
"Daedric Princes: Part 2 of 2" by @the-gray-fox on Tumblr: https://the-college-of-whispers.tumblr.com/post/661415471325855744/daedric-princes-part-2-of-2
Intense Jyggalag lore analysis by @spectralfeathers on Tumblr: https://the-college-of-whispers.tumblr.com/post/661585285574967296/orderwithoutmercy-thesheogorath