What are the origins of the two powers? What are they like, beside hating each other and one being evil for evil's sake and one being good beyond reproach (pure good and pure evil are incredibly shallow, by the way).
You also do not explain who sends the mages there to that plane, and why Zardikan never tried to use the connection to assault the other side.
Also, check the spelling, and break up huge blocks of text into paragraphs to make the text more legible. Some of the sentences are incomplete, too.
'A millennia' is wrong, as the singular is 'millennium', etc.
Plus, please finish one thing instead of dumping a dozen in-work ideas.
There is no !space! reality behind this one. There indeed was a divine womb from which sentient "suns" sprang forth, beings that happen to roam the sky, shed light for creation, and at night, they actually go home, dim, cool down and drink tea with dad.
This being a "fantasy" sub, it is about a world where this is reality. There is no orbit, there is but the sky, and in it three suns. They fly because they are divine. They shed light for the same reason. You could measure the power of the sun, but the reading could be "317 milliJesus" or something like that. It's just that in that world they never heard of our savior, they have their own.
So. Unthar is an undead divine entity. Those do not fly in elliptic paths around anything. It is locked in a real sub-dimension that is the Houses of the Dead, where you could sneak in and chat up your dead grandpa. It has a mind.
So. Suspend disbelief, there's lots of stranger subs than this one inthe citadel. Go to Comment
It can be a fold in space.
The N-th dimension above mundane reality.
The lint in the navel of the Vogon Lord of Poetry.
A computer simulation.
The inside of an effed-up bag of holding.
The biggest holo-deck ever built gone haywire.
An existence created by the eternal dream of Bakuki the Slime Prophet (you can enter it by getting stoned on a joint dipped into his mucus).
It could be a reality before our time, before the universe was remade into what it is now.
An alternate reality.
On the other side of a black hole.
Being open-minded does not make the brain fall out.
Also, the fact that a submission does not fit into one setting does not mean it requires a compatible explanation, nor is it a flaw of said submission if it comes without such a compatibility pack. Go to Comment
I did not give Unthar a motivation per se - it's a stillborn undead sun, an aberrant force of nature. But the room for an actual agenda is there - the dead sun may want something, and its escapes may have meaning (with the true horror being revealed once the consequences are understood).
The sub has two great elements - the description of the chase, and the idea that the Mordanfey's abilities are limited when it's being watched.
As for the unicorn, methinks it was always kinda neat, but this is an interesting twist. Go to Comment
Under the sewers of a large town ancient burial chambers are discovered. If the PCs investigate they fill find that a pale white flowers grows amongst the graves, in the dark.
How do they survive without light? What is their origin? Why in a burial chamber and not just in any old cave?
Can they be sold or do they have any special quality at all? It is up to the PCs to discover.