Villain / campain ideas for the Radiant Citadel?

Hi all, I am running a Radiant Citadel campaign, with a couple of homebrewed elements thrown in. I don't really like the "adventure anthology" style of adventures, so I'm trying to write an overall narrative to tie everything together. I'm looking to introduce a sort of cosmic villain, who is a big threat to not only the D&D multiverse, but the Radiant Citadel itself. Do you have any campaign ideas or villain ideas for this theoretical campaign?

Simplest option would be some sort of villain who needs to also access all the places afforded by the Radiant Citadel, maybe to collect some ancient item or lore that has been separated amongst the planes for whatever reason. Depending on the nature of the villain would inform what they might be after and why....and maybe why the party would care to stop them?

EDIT: Thee are, what 14 adventures in that book? So maybe consider the Rod of Seven Parts as a thing that was scattered across all the places connected to the Radiant Citadel.  That way the party could, in theory gather one part every other adventure or have the enemy score the item instead. Why your villain wants this powerful artifact is unknown. Maybe they want to corrupt it, or use its power to force some great change on the multiverse? 

EDIT EDIT: From the wiki,

Restored to its complete form, the rod held the power to kill Miska the Wolf-Spider or to release it from its prison.

Miska, the Wolf-Spider, was a demon lord who was once the Prince of Demons.

As a demon lord, Miska had a wide range of powerful abilities, from those common to all tanar'ri, to regeneration, and great strength and intelligence as befit his role as the Queen of Chaos's general.

Seems like a villainy thing to want to do?

That does seem like a pretty villain-y thing to do!

Before I learned what the Concord Jewels did, I was thinking of having the villain get the party to steal one somehow, which would give them the power to traverse planes, which would also make a pretty good villain. But, alas, the Concord Jewels are more like trams than anything. But I still think some sort of villain along those lines could be interesting!

Quote from RobynTheDM >>

That does seem like a pretty villain-y thing to do!

 

Before I learned what the Concord Jewels did, I was thinking of having the villain get the party to steal one somehow, which would give them the power to traverse planes, which would also make a pretty good villain. But, alas, the Concord Jewels are more like trams than anything. But I still think some sort of villain along those lines could be interesting!

 Maybe be the concord jewels are more then trams. Silly mortals have been using them to go back and forth to the citadel, when really they’re stolen from the crown a a dead god someone is trying to revive. Or they’re the phylacteries of a coven of liches. Or anything else you want them to be. 

Journeys Through the Radiant Citadel is originally an adventure anthology, meaning each adventure is a separate, self-contained story with its own characters, conflicts, and locations.

I decided to turn these individual adventures into one overarching campaign by introducing a central antagonist named Nal'Zirith, the Master of the Keening Gloom.

Nal'Zirith isn't interested in conquering the world or destroying civilizations. Instead, he is fascinated by mortal emotions and wants to understand how suffering influences people's decisions and actions. He secretly manipulates events throughout the different adventures, treating each situation as an experiment.

The players become his primary subjects after he takes something precious from each of them. Throughout the campaign, they investigate disturbances across different civilizations, gradually discovering that these seemingly unrelated events are connected to Nal'Zirith.

For example, in Salted Legacy:

The original adventure revolves around a family dispute between two rival market families, with Kasem's anger toward his brother's departure contributing to the conflict.

In my version, the adventure plays out almost exactly as written. However, I've added one underlying detail: Nal'Zirith has been subtly influencing Kasem's anger, intensifying his feelings of abandonment and resentment.

Nal'Zirith wants to observe how anger affects Kasem's decisions and whether that anger ultimately destroys his relationships or leads to reconciliation.

Regardless of how the players resolve the conflict, Nal'Zirith gains something from observing the outcome.

This is how I connect the entire campaign. Each adventure retains its original story, but one small element ties it to Nal'Zirith's larger experiment. The players can enjoy each adventure independently while slowly uncovering the greater mystery connecting them all.

The ultimate goal is for the players to confront Nal'Zirith and reclaim what he took from them.