Nightmare dodged the latest round of fireballs, grinning as she did so. "Seems like old times Luna. Your anger is delicious, it tastes like honey on my tongue." She sent a blast of black fire back to the attacking princess.
"THOU WILT ADDRESS US AS PRINCESS, YOUR MAJESTY, OR IF THOU WISHEST, THOU MAYEST SIMPLY BEG FOR THY LIFE! THOU HAST NO RIGHT TO ADDRESS US WITH ANY FAMILIARITY, DEMON!" She blasted each word, the Royal Canterlot Voice was more than a convenient way to address the masses. In the right hooves, it was a weapon, capable of deflecting attacks or driving back enemies. Luna used it to full effect, she supposed she could be heard for miles. Very well, let them hear the Princess of the Night destroying that which they feared. The wraith before her represented her biggest life's failure. She had given into temptation and accepted power from a dark and terrible entity. In that state she had waged a terrible war on her own sister, the only friend she had left in the world... Was it mere jealousy? Perhaps she had been angry at the world in general? Had part of her been bitter with Celestia for assisting in her second biggest failure?
Nightmare resorted to mist form for a moment to weather the worst of the sonic assault. "Come now "Princess", it wasn't all bad was it? You were angry, you wanted power, so you could act on your anger. I gave it to you." Nightmare smiled warmly. She gave a look to Luna, as a patient mother might look on a child who was throwing a tantrum for no reason, and knew it would soon end.
"YOU FORCED ME TO NEARLY KILL MY OWN SISTER!" She tore more of her creation from the sky, it was not visible in the waning day but the stars were ever there, they came at her call. She blasted the creature of dark fire with meteors and comets.
Nightmare scoffed. "Forced? I did nothing of the kind. I fed on your anger and returned it as rage and power! You acted on it, you came up with the plan to force eternal darkness on a world dependent on sunlight to live! Brilliant, by the way, imagine the starving ponies shivering in the cold, the despair in their eyes as they cursed you for an uncaring tyrant who doomed them because she felt "unappreciated". Oh, how I would have feasted on their sorrow. In the end, there would have been only you remaining, and I would have fed for eternity on your regret. Everything would have been perfect, if not for the elements which bound us both to the moon, and later separated us." She blinked from existence to reappear safely out of the path of destruction. She looked down. "Oh how wonderful, it seems somepony lives down there. This should be quite entertaining." She stared down in hunger, waiting for the coming death.
Luna looked down in panic. Her starfall was speeding towards an unassuming abode, built inside of a hollow tree in the middle of the woods. She sped forward to intercept it. Nightmare followed, flying close to Luna's ear. "Will you make it? Will you survive the blow? Will you have blood on your hooves because you opposed me? I can't wait to find out dear "Princess"..."
Luna whipped her tail around and struck Nightmare, who fell back laughing. She broke the sound barrier handily, and had she looked back she would have seen a growing wave of darkness spreading out in an explosion. For just a moment the sky lost its sunlight, and the night sky shone in all its glory. She threw up a barrier and simultaneously grasped the falling stars with her magic, altering their trajectory. They bounced of her shield and flew upwards into the sky, returning to their intended course in her celestial plan.
She turned to face Nightmare, who only grinned wider. "Don't you see "Your Highness?" You attempt to oppose me, and you only end up hurting the ones you love!" She punctuated this statement with another lash of dark fire.
Luna regained her bearings and glared hate at the abomination. "When I gave in I nearly killed everyone! You vile deceiver! You promised power and delivered hate and madness!"
Nightmare waved a hoof tauntingly. "I amplified what was there "Princess", no more. The hate you felt was your own. However you are past all that now aren't you? You love your ponies, you love your sister. You hate Discord, more I suspect than you hate me. Wouldn't you like the power needed to defend her, and all your subjects? I can offer you that. Join with me again Luna-" She specifically used the more familiar name now, regardless of Luna's stated wishes. "We could defeat him, you resisted a full bond when we last joined, if you give yourself to me without reserve we could easily best him. Think how everypony would love you, the savior of the entire world and of your own sister who you once attacked. One thousand years of distrust and fear would be wiped away in a single instant!"
Luna shook her head. "Never again, I would never be so naive as to trust you." She cast a fireball spell aimed at Nightmare's chest.
Nightmare cancelled the attack with her own ball of dark fire. "That is unfortunate, Celestia could have used the help. Oh look, isn't that her crashing now?"
Luna watched in horror as her sister was flung to the ground. "CELESTIA!"
-------------------------------------------------
"This could have been planned better." Celestia decided, coldly analyzing the battle as it progressed. She was not going to win, at best she hoped to buy time for the six to recover their elements.
"Come now Celestia, is that the best you have in you? You hardly seem to be giving this your full attention. Don't I warrant that courtesy at least?" Discord rained flaming rubber ducks from the sky, then tossed a bathtub full of snakes at her.
Celestia smiled apologetically. "How could I be so rude? Do forgive me dear, you were saying?" She aimed a precision solar flare at the draconequis. He gave a mocking bow and snapped his fingers, the solar flare became a spotlight.
Discord pulled a microphone from nowhere.
"Ahem. This is dedicated, to the mare I loved." His eyes twinkled. A brass band with piano accompaniment appeared, played entirely by house cats.
"At first I was afraid I was petrified
Kept thinkin' I could never live without you by my side;
But then I spent so many nights,
Thinkin' how you did me wrong,
And I grew strong and I learned how to get along!" He leaned into the mike now, putting on his most soulful expression.
"And now I'm back from inner space.
I came back to find you here with that sad look upon your face.
You should have changed that stupid lock,
You should have made a better key,
If you had thought those charms would ever have a chance to bother me!"
He winked knowingly while Celestia glared. He had once asked her to simply let him be, or even join him, professing admiration for the strong willed mare who dared to stand against him when all of her friends had turned on her. He suddenly swept her up in a waltz.
"So I go, I walked out the door
not turning round now
'cause I'm not welcome anymore
Weren't you the one who tried to tried to trap me for all time
Do you think I'd crumble
Did you think I'd lay down and die?"
The Waltz became a slightly quicker paced foxtrot, he always was a good dancer, even if he only did so to mock.
"Oh no, not I. I will survive
Oh as long as I know how to love I know I'll stay alive;
I've got all my life to live,
I've got all my love to give and I'll survive,
I will survive. Hey hey."
The band played for a while, and the foxtrot turned into a tango. Discord grasped a rose in his teeth and marched her across the sky.
"It took all the strength I had not to fall apart
Kept trying' hard to mend the pieces of my broken heart,
And I spent oh so many nights
Just feeling sorry for myself. I used to cry
But now I hold my head up high"
They completely one circuit, and Celestia grasped the rose from his teeth.
And you see me somepony new
I'm not that captured foolish villain still in love with you,
And so I felt like droppin' in
You did not expect to see me free.
Now I'm savin' all my chaos for your dear little ponies
Go on now..."
At the climax of the song he dipped her low, then grinned, smashing her straight in the teeth with his clawed fist. She plummeted to the earth creating a crater in her impact zone. "I told you once you would fall for me, did I not?" Discord called after her.
Celestia shook her head, dazed in more ways than one. She looked up to see a streak of darkness across the fading light of the afternoon. "CELESTIA!" Luna sped forward, aimed low, and arched high striking Discord in the jaw in a dazzling uppercut.
Discord regained his footing on a cloud some thirty hooves from the location he had been struck. He wiggled his jaw in apparent discomfort. He raised his voice so both could hear. "Really now, this has been fun but you both have to know you can't win here, what did you expect to happen? I am tired of pulling punches with you, I truly am. I won't be captured again, so why must we fight? I'm going to call this mate in one move unless you have something more up your sleeve."
Celestia rose from her kneeling position, and darted to her sister. They grinned. "Sister-" Luna said. "-perhaps it's time we changed dance partners."
Celestia grinned predatorily at the approaching Nightmare. A chance to lay hooves on the being that cost her one thousand years of loneliness? Oh yes, that was something to look forward to.
Luna smiled sweetly at Discord. "Shall we dance, chaos?"