The Battle of Moon - the story

Princess Luna looked up, deep in the darkness lurked an unforgiving foe that would soon emerge. She had spent many a day battling this netherworld beast, summoned by the darkness that first captured her soul almost 1000 years before, and yet every night it retreated in fear. The young Alicorn had never quite understood why it did this, considering it was a beast of darkness, but at least it gave her time to rest. For years Luna had fought this beast, and for years, both had stood undefeated. Wounded? Yes. But defeated? No. However, Princess Luna was adamant that she would destroy it before her 1000 years upon the moon was up. Mentally she prepared herself for another day of fighting, her spells were becoming weaker, but so was the beast, she knew the darkness that had bought her to the moon would once again take over and she could feel its stone like effects wearing on her already. once again, her sisters sun appeared and the princess knew that she was moments away from her battle, the fear that crept through her was not her own she registered, no, it was the darkness, the fears of Nightmare Moon. then it began to emerge, a grey green tentacle waving its was from a crack in the surface, feeling around to find a hook with which to pull itself up from the crack, and then it emerges, taller than the largest tree in the forests surrounding her old palace, more ugly than Discord himself, ("hey I'm not ugly, just a little different." Discord its a 'metaphor' deal with it "fine...but this conversation isn't over") with one eye menacingly staring at our dear Luna, and its skin scattered with cuts, bruises and scars from their battles. yet today felt different, yet she couldn't work out why, but today felt like a victory was in hand for one side or the other, readying herself for the first spell, the beast charged, switching spells she disappeared, momentarily confusing the beast, but allowing her enough time to reappear behind the beast with an attack spell, one that she had been repairing for weeks. a spell that required more thought was difficult and need time to charge. time was not on her hands, her horn began to light up first, the spell lacing its way around her weaving a glowing barrier of magic, and then finally, one last push and Luna released it, a full blown attack, a combination of several different spells that normally would drain her both mentally and physically when used together, yet this spell would hardly affect her, aimed straight at the beasts heart, it would penetrate its skin, and not only stun it, but begin to attack it from the inside, hopefully, allowing her to find its weak point. Finally, the spell was ready to use, and she let it fly, wisps of coloured magic forcing themselves towards the beast, yet something was not right, the beast was still moving. Fast. And it was nearing towards her, this had to work, she couldn't let the darkness win. One... Two... Three... the beast lashed out, barely missing the hairs on Luna's nose her spell spluttering to a halt. 
"But? that should have worked. I worked on that for weeks!"

the beast straightened up "You... you... cannot... beat... me... not... with the... the... darkness... within..." it growled at her

Shocked she tumbled back giving time for the beast to attack again, struggling to stand, she covered her face with her hoof, but no blow came. instead, the bubbling laughter of... an earth pony. and earth pony? in space? and yet there she was, a pink pony with three ballons on her flank and a fishbowl over her head. laughing at the beast, now toppled as if a statue on the surface of moon.

"Just a little Bish, a lot of Bash and a smidgen of Bosh, easy as cake really, mmmn cake, do you want some cake? or sweets? Everypony likes sweets... she carried on muttering like this, bouncing on the surface of the moon as Luna just watched, here, on the moon, her moon, was another pony. which meant something. Princess Luna would be returning to Equestria. To her throne.

Nightmare moon would be returning to take revenge. The battle on the moon might be over, with the aid of a strange pink pony, but the battle of the moon, was only just beginning,