D&D 3E/3.5 Theoparts of Tharizdun

[Gravenhurst48]

Yes, a never ending story.
Check link, the Forgotten Yemle, sorry, is a 1st E D&D module.

The Forgotten Temple of Tharizdun - Wikipedia

en.m.wikipedia.org

Ok, dragon your idea. Shothragot is in Elder Evils handbook. The dragon also may have been mentioned in the Forgotten Temple. I need to stop playing AC Odyssey and look up these references for everyone.

 

[werecorpse]

One way to use the theoparts Idea with a twist, one which relies on having a stable playing group is
A) Run a standard campaign in one world (say forgotten realms - princes of apocalypse or out of the abyss) but add in a bunch of magic items that can be combined to make an uber item around the time the campaign ends ie a ring of warmth, a wand of binding and a broach of shielding that can be fitted together with an unusual black diamond to make a thing that takes up one attunement slot for all powers and additionally evards tentacles & disintegrates 2/long rest; then
B) Run another campaign in another realm say a dragonlance one where the new party also finds a bunch of items that can fit together to make one uber item, again requiring a black diamond; then finally
C) Run your final campaign - in Greyhawk where the world is suffering from nightmares and far realms shenanigans leading at some point the party trying to stop the bad guys from assembling the third of three theoparts because the first two have been accidentally assembled somewhere else in the multiverse and if the third is assembled the three uber items (or theoparts) can be used to unchain Tharizdun which will end the multiverses (in part because Asmodeus “binding” ability will fail, fiendish contracts will have no force legitimacy, leading to devils abandoning the blood war and siding with demons in destroying the multiverse )

Apart from introducing the uber magic item in each of the first two campaigns you don’t really need to do anything. But if you do it, it really is playing the long game.

 

[Gravenhurst48]

One way to use the theoparts Idea with a twist, one which relies on having a stable playing group is
A) Run a standard campaign in one world (say forgotten realms - princes of apocalypse or out of the abyss) but add in a bunch of magic items that can be combined to make an uber item around the time the campaign ends ie a ring of warmth, a wand of binding and a broach of shielding that can be fitted together with an unusual black diamond to make a thing that takes up one attunement slot for all powers and additionally evards tentacles & disintegrates 2/long rest; then
B) Run another campaign in another realm say a dragonlance one where the new party also finds a bunch of items that can fit together to make one uber item, again requiring a black diamond; then finally
C) Run your final campaign - in Greyhawk where the world is suffering from nightmares and far realms shenanigans leading at some point the party trying to stop the bad guys from assembling the third of three theoparts because the first two have been accidentally assembled somewhere else in the multiverse and if the third is assembled the three uber items (or theoparts) can be used to unchain Tharizdun which will end the multiverses (in part because Asmodeus “binding” ability will fail, fiendish contracts will have no force legitimacy, leading to devils abandoning the blood war and siding with demons in destroying the multiverse )

Apart from introducing the uber magic item in each of the first two campaigns you don’t really need to do anything. But if you do it, it really is playing the long game.

I like the storyline with ending the Blood War between devils and demons, though that war has ended for me eons ago, I never came up with any real reason why the Blood War ended. It was more in my head, as players never questioned that backstory because I never ran any adventure in Planescape, so it never came up.
Interesting to have the Theoparts join lesser evils to do the Chained Ones dirty job. But, in Gord's novel story, the demons are collecting the Theoparts just to gain an edge to destroy their other demon opponents. I doubt they would join devils to end what they gained control of, say, all the Abyss under one Demon Prince to give it to a imprisoned deity they may not know anything about.
Also your three worlds mess up continuity too, because the Abyss in each world is a different Abyss in each Cosmology, so the Demogorgon in each Cosmology may not agree on the same direction with joining a Theopart to free an imprisoned deity. Most likely, each Demon Prince would try to control the other or war with the other cosmology Abyss to gain even greater armies, etc.. Now that is an infinite supply of demons and a better "True" Blood War amidst just demon kind.
Also the Theoparts exist only in the Greyhawk cosmology, though there could be a different object identified as an Elder Evil artifact for Tharizdun in another world's cosmology.
But the game is your oyster, you can do whatever makes your campaign story make sense and cool.