Today I got to thinking whether Nehelenia might very well have been the original Queen of the Moon under Chaos who was banished to the Moon's interior/dark side.

This came to mind on the basis of her having been present at the time prior to Usagi's birth wherein she seems to know Queen Serenity from a time before Silver Millenium. Likewise, the arc itself is alternatively called the Dead Moon Arc which gives credence to the possibility that she may have reigned over a more malevolent Moon Kingdom in relation to the Earth, whereby mortal men lived in fear of the inhabitants of the Moon (which would explain the uprising during Silver Millennium. Metallia sought to get revenge for Nehelenia being banished and sealed away.). 

However, what struck me was that Nehelenia was able to enter Elysium undetected. Some part of me suspects that at one time or another she had a unique relationship to the people of Earth which so allowed her that sort of access. After all, how did she manage to awaken the Amazon senshi from the future, or know of their presence?

Barring her having been the previous ruler of the Moon, it would be nice to learn that she was the former advisor to Queen Serenity from a race of beings who lived in a world of mirrors. This would explain why she was as skilled in creating glamours and other illusions.  I also like the idea of her alternatively being a relative of Mamoru's, but that would only further complicate things.

I've heard a lot of different theories for Nehelannia and I have not disliked a single one yet.

I like this idea now too!

I've never heard of a theory of being possibly related to Mamoru. Can I hear more about that because I can't seem to wrap my head around it?

Well I've never quite given it much thought, it was just what came to mind when I was typing out my response.

She bears some sort of resemblance to Mamoru, so perhaps she was once intended to be the Mistress of Elysium, but that changed with the birth of Usagi? I wanted to suggest that she might be Mamoru's mother, but I don't think that works given that I believe we're meant to infer that Mamoru was born in the same way that Serenity was, by virtue of the Golden Crystal's wielder's (Helios) desire. So that really only leaves the possibility that she may be some sort of relative of his who ruled in Elysium and thus knew of, or was the rightful heir (once upon a time) of the Amazon senshi.

She's based off of Nehalennia:
https://en.wikipedia.org/wiki/Nehalennia

What other theories have you seen going around concerning her?

Hhmmmm....

So she came from a distant place like Queen Serenity... but could she be refering to a far off time?

She resembles Mamoru and Chibiusa.

Maybe, she is Chibiusa and Helios's daughter from a far off future that some how got trapped and lost within the mirrors, ending up traveling into the far past and into the silver millennium where she meets her Great Grandmother and ends up cursing her Grandmother unknowingly.

It was hinted at that she became enamored with Helios. 

It would be similar to her 'mother' since chibiusa had a crush on Mamoru.

It would explain how she knew about the Asteroid Senshi that aren't supposed to wake up until Chibiusa completed her Senshi training and went back to Crystal Tokyox nearly 1000 years later.

This would make the family bonds make sense.

She is related to the moon as we see her crescent moons and she is related to the earth, not through dreams but nightmares. Her father being influenced by dreams.

I really like this!

It really depends on the version. For the manga, I thought she was the mirror opposite of Queen Serenity. like a shadow of the light. Basically Queen Serenity ruled the kingdom of the white moon (Full) while Nehellenia ruled her own kingdom of the dark moon (New) which was probably sealed away with her when she attacked the Silver Millenium, and became the Dead Moon Circus. She was freed by an intense Solar Eclipse, which is only possible when the moon is in its new phase, and the darkness was strong enough for her to inflict her will on Earth and Elysion.

The manga never goes into detail so it's up for speculation.

It's implied that neither Queen Serenity or nehelannia were from the solar system/time.

Queen Serenity is the one who sealed her away and she managed to break free during the eclipse in the present from that seal. 

She was sealed when Princess Serenity was still just a baby and she only became free after they were all reborn and had already been fighting for such a long time in the present.

It was explored more in the anime but it was implied in the manga she used mirrors to move between dimensions. 

This ability could have helped her further the power to eventually fully break free of the seal but I don't remember if the details were said about how she broke the seal...


MIND TWISTER! Maybe...

Am I remembering correctly here or not... but did the manga at one point imply they hid from the sun or some kind of celestial body's sight? Someones sight?

Can someone scan the page if its there?

"maybe Serenity felt kind of guilty being a queen if her sister couldn't, and so partitioned the kingdom, but then Nehelenia just felt she got the short end of the stick."

This would actually go along with the Roman mythology where Zeus ruled Mount Olympus but his brother,   Hades, was given the Underworld to rule and Hades always resented his brother for doing that. We all know how heavily based Sailor Moon is in Roman/Greek mythology.

I hadn't really given this much thought, but I like the idea of Nehellenia's knowledge and manipulation of Helios being related somehow to a bond she might have with the Earth. If only we knew more about Elysion, particularly when it comes to entering that realm and causing any warnings/etc.

I also like your mention, Crescent.Moon.Rose, referencing Greco-Roman mythology for the relationship between Nehellenia and Serenity and mirror Zeus/Jupiter and Hades/Pluto. That's an excellent point!