Marelin and the Mane 6 and the battle of Canterlot
It was the night after the Ponyville's party celebrating the fall of the Storm King. Almost every pony was asleep in their homes, barns, and stables. Even the four princesses, guardians of Equestrian were sleeping as the effects of their magic being drained and returned finally caught up them.
Celestia briefly woke, only to raise the sun before falling back asleep. Perhaps if the princess had remained awake, or if the return of her magic hastened by even a scant few minutes, the arrival of a new, and far more powerful foe might've been stopped. But she did not, and it did not.
And so, far below, where the Storm Kings stone remains still lay scattered and smashed to dust, a pony swathed in a dark cloak entered slowly. The ponies hooves clopped metallically against the cobblestones as it approached the largest jet-black piece of the Storm Kings head. The pony delicately placed one metal-shod hooves on the piece. The shadows seemed to thicken for a brief moment, and a whisper came, words carried on a gasp of wind. If some other pony was there, they would have recognized the gruff and deep tones of the creature known as the Storm King.
"You're here?…. But why?"
The cloaked pony snorted delicately, and using one metal shod hoof drew aside the voluminous cloak that obstructed much of the pony form and tapped at a large gem shaped depression in a[ obsidian colored bread plate.
The Storm Kings whispered voice came again.
"The staff was yours?"
There was a pause before the Storm King's voice came back, high and panicked.
"I swear I didn't know!"
The pony seemed to shrug before again placing one hoof on the largest piece of the Storm King's head.
"Wait wait wait! ITs not my fault! Tempest is the one who stole your staff!"
The hoof paused, and in a rush the being formerly known as the Storm King told the mysterious pony the whole story, strangely not leaving out a single detail. Once the Storm King was finished, there was a pause, thick with silence, and then the cloaked ponies outreach d hoof began to grow with a bright, eerie white light.
As the light shone, the Storm King's head began to rebuild itself, piece by piece, specks of dust congregating into bigger pieces that slotted themselves into place. And as reconstruction continued, a neck began to take form, and the Storm King began laughing, but then the upraised hoof came down, and the Storm King began screaming. The hoof came down in a burst of white light that shattered the head of the Storm King, rendering it into dust, and a gust of wind that scattered the last remains of the Storm King across the city.
The Storm King managed to get in one last for, though choked and garbled.
"D-damn you Marelin… Damn you, mother."
That last gasp of wind blew back the pony's hood, revealing a jet-black mare with eyes and mane the color of fresh, pure snow.
The mare sighed, the sound small, and resigned. A hoof glowed once again as the mare began dragging her eerily glowing forelimb through the cobbled streets.
The next morning the four princesses awoke to the low, steady murmurs of a large crowd of ponies, clustered around a message gouged directly into the stone cobbles of the courtyards underneath Canterlot.
'The Storm King stole my staff. You now Have it. I will return in three days to reclaim it.'
Below the message was a design that had also been torn into the courtyard, it was an image of crossed staves over a simple tree.
Celestia turned to Twilight, with a harsh look that seemed out of place on the normally kind and gentle ponies face.
"Go find Tempest. I need to have a chat with your new friend."