Okay, so, I have already made a story relating to this, but I'd like to here your opinions on this hypothesis I have. Here it is:

While we all know that Celestia and Luna were famous for many acts 1000 years ago, at one time Luna had her own charges that she cared for on the Moon. With the moon having many different conditions to the land of Equestria, Luna blessed her charges with gifts that would allow them to operate in her kingdom. She gave her charges of all three mortal races the ability to see in the dimmer light that shined on the moon, so their eyes became adapted for night, should they visit their neighbor home in Equestria.

Also, with winds being weaker on the Moon, she blessed her charges who were of Pegasus decent with wings more suited for her kingdom, hence why they took on a bat like look to their wings. And with it being a little bit cooler on the moon, she made their fur more... fluffy to keep them a little more warm.

She of course never had any rejection of her subjects taking a leave of absence to visit her sister's neighboring Kingdom, since some did have family there, and she of course would visit her sister.

But then one day, there was an attack, by a unicorn stallion the royal alicorn sisters had trusted. King Sombra of the Crystal Empire. Why he'd attack her kingdom without cause, she did not know for sure, but had a pretty good guess, when she saw his appearance had changed to something dark. She and her Lunar Guard Fought hard as Luna sent a distress call to her sister. Celestia did come to help, but seeing as Sombra's forces outmatched even the force Celestia could bring with her along with her sister's guard, they knew they had to make a retreat. Getting all civilians of the Lunar Kingdom safely to the land of Equestria, a few guards sacrificed themselves to save their ruler. Equestria needed it's rulers, even if one operated in the heavens above.

After they left, what remained of Sombra's forces after the battle, made their retreat back to the crystal empire. Luna wanted revenge, but she also knew that she had to protect her and her sister's charges. That meant defeating Sombra for the sake of the ponies of Equestria. But his defeat would have to wait, because Sombra's attack had alerted other chaotic beings that started to see Equestria was still vulnerable. Thankfully, with the help of the Elements of Harmony, Celestia and Luna were able to eliminate the threats and keep them under control, including Sombra.

After all was set right, Luna suggested to Celestia that there should be some monument or something that dedicated the brave souls who gave their lives to protect their fellow ponies, including their leaders. Celestia was of course all for it, but parliament was not and denied it. Luna was a little torqued by their refusal, but she kept a level head.

But then, things started to take a turn for the worst. As Luna began to see how her charges were coping to their new home in Equestria, what she saw was beyond reason. The three pony tribes were treating her charges like dirt beneath their hooves, just because they looked different. Some of her charges were being physically harmed even. Of course non of Equestria's subjects knew she had been watching. She took this up to parliament, and they cast her argument aside, acting as if they were saying her charges weren't being targeted.

This was the last straw for Luna. With parliament pretty much telling her they did not respect her, and showed little care about her charges, her rage soon consumed her. But that rage also blinded her to the truth. With her darker side having won her over, she felt Celestia was somehow involved, seeing as politicians and other ponies seemed to respect her and never call her actions into questions as they did with Luna.

Soon that darkness was so great, that her form took on a darker and more sinister tone. And you all know the rest.

But what happened after Nightmare Moon's defeat? Celestia soon discovered what had turned her sister, and dealt a swift change to how Bat Ponies were treated. Never again, would one race be treated lower then the other. Of course some families would not let their old habits die, but the bulk of the targeting was soon null and void.

So, what do you think? Did she become Nightmare Moon for a good reason? I mean, someone treating my kin that way would push me over the edge.

Interesting theory though if it is how that happened the only problem is Sombra. He never attacked Equestria nor did they even know who he was. He wasn't King Sombra until he shattered the real ruler of the Crystal Empire and a possible long time friend of Celestia's, Princess Amore who judging by the name might be related to Cadence, especially cause Cadence has the Crystal Heart itself as a cutie mark. Anyway he took over the Empire after the pain the Crystal Heart caused him and encouragement from his mother so his kind could be free to take over the world itself with the Crystal Heart shattered, something that was prevented for 1000 years before finally happening sometime before Flurry Heart is born. His marefriend Radient Heart, and Amore tried to reason with him to no avail and Radient had to go to the princesses in hopes they could fix him. We all know what happened afterwards. The Empire is banished to spite Radient and she stopped her training with Celestia til after recent events.

5535716 ah that only happen in the comics and the they count as b canon. B canon is not canon think of it as AU.

5535843 Yet the writers of the show consider it and Seige of the Crystal Empire canon to the show I hear. Apparently they like how Sombra was reformed there and don't want to mess it up so he's not being used in the show anymore. Guessing that might mean any future appearances outside of AUs like that War timeline, the past and references to his actions are out now.

Plus they just connected an issue of Friends Forever to the show with the newest EP, specifically the flight school reunion which was a comics only event. Twilight mentioned it while waiting for her friends.

5535878 oh so now the writers connecting the comics to the show? and how long it took them to mention them....

5535716
5535843
I only follow what the show puts out, so anything put in the comics is null and void to me till the show dictates otherwise. But it's fun to have theories that will probably never be canon..... or will they?

I don't we've even had such things as bat ponies or "Thestrals" appear in FiM canon proper, from what I can tell, it just seems that some people ran wild with the appearance of Luna's chariot guards in S2.

Personally, I think Moonie surfaced for both a very good reason, but also several really selfish ones, she wouldn't be a villian otherwise!

I like to think that Luna was entrusted with keeping the night safe from predators and monsters that like to lurk in the darkness. I like to think that her probably monumental efforts in keeping back various horrors that waylaid early equestria were unrecognized and possibly even looked on with contempt by the populace, after all, she'd have to screw up sometimes, which would cause some (or maybe a lot of) ponies to die.

Of course, in my dark and edgey as fuck headcanon, the pony populace would have to be as dimwitted and petty as they are often shown as such in the show.

Either way, my basic theory can be boiled down to Luna not getting proper recognition for great efforts that she did, this also ties in nicely with Moonie's desire for eternal night, as that would quite nicely eliminate all those "petulant ponies" that refused to honor or rejected her.

5536430 Actually this was more based off of Flutterbat.

5536809
yeah fuck flutterbat

5537047 I don't know, I think Bat Ponies look cool, but that's just me.

5535566 My headcanon is that the sole reason Nightmare did what she did was to please Luna, not realizing that Luna detested every moment of it. To her it didn't matter who suffered and who didn't, what was kept and what was lost, what was right and what was wrong, as long as Luna had a smile on her face.

Sorry if that was mentioned already, but I want to share my ideas.

So, we know from the daybreaker episode (royal problem if i remember correctly) that neither Luna nor Celestia appreciate each others duties or at the very least don't understand how hard it is. Also Celestia said herself that everypony is asleep at night, so Luna always works completely alone.

Now, and admittedly that is because of my headcanon that Nightmare Moon is a separate entity instead of a second personality, Nightmare Moon felt how alone Luna was, how much Luna longed for someone who appreciates her, and how jealous she was. So Nightmare Moon decided to show herself to Luna, and only Luna, at night, to simply be a friend to her. Sort of a symbiotic possession,Nightmare Moon gets a host, and therefore live, and Luna a friend.

As Luna grew more jealous, Nightmare Moon shared her feelings. NMM just wanted to be a good friend, so after a particularly harsh argument between Sunbutt and Luna, NMM decided to force Celestia to appreciate Luna more.

She tricked Luna into freeing her and letting NMM take over, and NMM then attacked Celestia. Her ambition was to show Celestia first hoof how hard it is to battle nightmares every night by turning Celestia's live into her worst nightmare.

But she forgot to account for the elements of Harmony, so before she could reveal to Celestia how bad of a sister Celestia was, brining her sister so far as to form a friendship with a Demon because no pony bothered to, she was banished.