Ponykind as a whole had faced many challenges and disasters. Some where lost time; others immortalized in myth and legend. But it left many with the feeling they could overcome anything.
Magic itself failing was a new one, though.
Books, furniture and socks rained from Cloudsdale as the city dissipated, the alarmed inhabitants having to alternate between falling and gliding to get to the ground as flight and cloudwalking suddely seemed to be out of their grasp.
Farmers and gardeners freaked out across the entire country as they no longer could hear the wordless whispers of animals, nor the simpler vocabulary of plants.
An annoyed cockatrice tried to petrify the oblivious rooster that kept singing nonstop, interrupting the chimeric creature's nap. The lack of success only made it crankier as it gave up and simply chased the annoyance away from its home.
Screams of terror filled most cities as unicorns found themselves incapable of levitating even the smallest object. Judges, police officers, thieves, teachers, students, nobles, chefs, librarians and more cried in fear of having to use their hooves and mouths to interact with objects.
Pegasi, Earth and Crystal pony alike rolled their eyes at that.
Dragons gathered in confusion and agitation as they felt their magic fires die down, leaving behind only their normal blaze.
Changelings ran from mobs carrying pitchforks and torches, their disguises shorting out entirely. Chrysalis especially was alarmed when she turned back to normal in the middle of Shining Armor and Cadence's picnic, falling from the tree she'd been spying them from as a cat. Right over their food.
Back in Canterlot, the Royal Sisters were calmly freaking out at the realization that, try as they might, whatever magic they could muster couldn't reach the sun. Reaching out to the moon proved the same.
Los Pegasus just suffered a slight malfunction in the casinos. A pegasus didn't complain as the glitch allowed him to win the big prize.
The Griffins and Yaks were too busy competing in Griffinstone's stadium to notice the disaster at first, but it was only a matter of time.
The Everfree shuddered, the entire forest feeling its protection against the arcane forces of other magics slowly becoming inert. Both the deers and the less sapient inhabitants were unnerved at the current development.
The Tree of Harmony found itself growing tired, feeling for the first time the need to sleep. It didn't like that one bit.
All across the world, similar things happened. The planet had been filled with magic for countless eons, and it had thrived with it. If the problem grew... well, life as everyone knew it would be over. And a dark age would befall them all.
A few hours later, the situation had only grown worse.
Reports from all of Equestria and beyond -whatever managed to arrive in sudden bursts of arcane power as the spells struggled to work, anyway- showed this was happening everywhere. Every country, every kingdom, every nation that used magic told the same.
'Magic is failing.'
"This is worse than we feared, sister," Celestia said. The alicorn was becoming frantic at the current situation, something a small part of Luna found nostalgic as the rest of her tried not to panic with her sister.
The royal sisters were in their private study, going over both their private collection of tomes about the magical arts and the slowly growing pile of messages informing them of the chaos outside, and begging for help or guide.
Luna slammed a book in her desk as she grabbed a small note that had just formed in front of her, the spell transporting it stubbornly pushing forward in spite of the current disaster. "I know. I have all of the librarians, mages and scholars searching every single book and tome in the city for a cause, or even a lead to the source. So far, they got nothing."
Celestia opened a scroll and quickly read through it- before stopping and rereading a crucial part.
"... I think we just found one. Look at this this."
Luna took the scroll in her hooves, not for the first time wishing her telekinesis worked. "Los Pegasus is still standing?! I thought it would have dissolved as every other cloud construct has."
"And spells seem to be mostly functional in the city so far," Celestia pointed out. Her mind recalled something, and she dove for the growing pile of scrolls and letters, looking for something in particular.
"I know that look. What is it?" Luna asked as the white alicorn jumped out of the pile with a letter between her teeth. She wasted no time opening it and going through the content at a speed that would have made Twilight jealous.
"The report of the Garrison on the shores of the South Lunar Ocean."
Luna's expression soured, anger growing on the alicorn. "Discord," She muttered. "I should have known."
"There's nothing new to report about him, but they do mention a small accident or two when spells lose strength for a second."
Clearing her desk of papers, Luna grabbed a map and unfolded it, going over it with her sister.
Los Pegasus was on the southwest of Equestria; the princess' hoof passed over the city and towards the west, stopping at the point where the garrison was stationed. A couple of miles to the northwest was one of the biggest headaches she had known in her life.
"So, the closer to his castle- the closer to him-, the lesser this... arcane failure?" The princess of the night conjectured.
Celestia hesitated. "It's too early to assume that, and we know too little... but it's the only lead we have so far."
"Then we know what to do."
Four Days Later
Nerves rattled, bodies exhausted at so many days of travel at hoof (the western winds not letting them use the balloon), discussions and screams directed at each other due to their current mission, the utterly alien feeling of their magic not responding...
The Bearers were not in a good mood.
But they had done it; near the coast a red castle rose from the ground, the towers dancing in the wind like flowers under a gentle breeze.
Undeterred, Twilight advanced, the others following behind as their Elements began to lose their dullness, the gems glittering back to life. The six ponies were relieved at that, some expressing it more than others.
As the group walked towards it with Rainbow flying over them for the first time in half a week and Pinkie finding the strength to bounce, a board quickly floated towards them.
WELCOME TO THE SHIFTING ROCK!
HOME OF THE ONE AND ONLY DISCORD!
Blue and white alicorns not welcome.
The owner and inhabitants don't make themselves responsible for any physical and/or psychological damage suffered inside the castle's premises. It was your choice to enter :P
Author's Note
And here I come with yet another story for you 
mrsupercala requested this, so thank him for the idea :D
This is unconnected to my other stories, and takes place between Season 3 and 4.
MLP belongs to Hasbro.
The ponies were now standing in front of the castle, resolute on entering, even if their reasons weren't the same. Their strong wills pushed their tired bodies forward; the road had been long and hard without their then absent powers; but now they had them back, so their spirits were rising.
And yet, there was another obstacle in front of their daring crusade. After a minute of standing heroically in front of the entrance, Applejack decided to voice the obvious question.
"So, how do we open the door? Ah don't see the doorknob."
Rainbow flew to the gate and tried to pry it open, only for it to fell forward, smashing the pegasus on the soft ground before standing back up.
"Well, I tried," came her muffled voice. "Who's next?"
Pinkie conjured her party cannon for the first time in days; after a gentle, amorous kiss on the side of her precious tool/weapon, she aimed it over the walls of the castle and prepared to introduce herself on the cannon, ready to shot herself over the stubborn rocks and wood.
Dozens of cannons deployed over the walls, fires and waters shifting inside as they aimed at the perceived menace, causing the ponies to shrink back. Pinkie smiled nervously as she dismounted her party cannon and put it away, the ones on the castle vanishing as their inferior brethen stopped aiming at the Shifting Rock.
Twilight tried to teleport the group past the door, only to be pushed back mid-teleport by an annoyed protection field, appearing ten steps farther from the castle than they were before.
Rarity simply brought out a small mirror and a comb from her bag and fixed her mane. The rest just stared at the unicorn, who shrugged apologetically. "I'm afraid I don't have an idea on how to enter, darlings."
The group then turned to Applejack and Fluttershy.
"... Ah got nothin'."
"... Saying 'please'?" Fluttershy suggested timidly.
Before her friends could groan at the apparently useless suggestion, the door slid open. The six ponies just gawked at the entrance.
"... What would you know? That is the magic word," Pinkie mused as she bounced forward.
A whirlwind erupted from the entrance and landed in front of them before dissipating, a feathered reptile now blocking their path.
Of green scales and blue plumage, he stared back at the Bearers, adjusting the bag over his shoulder before bellowing.
"I am the Gatekeeper! Who dares enter the Shifting Rock without knocking first?!"
Silence reigned for a moment before Pinkie applauded at the dramatic entrance. The reptile looked at the small group before recognition flashed in his eyes.
"Ah, the Bearers of the Elements of Harmony."
"How do you know who we are?" Rainbow asked suspiciously; it was the first time a stranger recognized them for that.
"You mean apart form the fact that you are wearing them right now?" He deadpanned pointing to her neck.
"Oh."
"I read the newspaper every day; you have been mentioned a couple of times."
"A couple of times?" Fluttershy asked, embarrassed at the idea of making the headlines.
"Only a couple of times?" Rarity lamented.
The Gatekeeper cleared his throat and adressed the group in a stern, formal tone. "You may have convinced the castle that you have no ill will by being kind, but none can be allowed to enter! This is a very important day!"
Rainbow and Twilight managed to take one step forward before Fluttershy blocked them, asking them to let her handle this. She then walked towards the reptile.
"Hello, mister Gatekeeper; I'm Fluttershy, Discord's friend."
The Gatekeeper looked at the pegasus before producing a small notebook from his bag, flipping through the pages. "Ah, yes. The Spirit of Chaos had extended an invitation to you in the past, leaving very clear that you are always welcome.
"It is an honor to meet the pony willing to see beyond the visage of my master and see the heart within."
He bowed before the slightly blushing pegasus before continuing. "But I'm afraid I must reiterate my previous statement: this is a very important day. The Spirit of Chaos has asked to not be disturbed."
"Ah'm afraid we have to insist, Gatekeeper."
Twilight stepped forward. "Gatekeeper, something terrible has befallen almost every land known except this place. We need to talk to Discord to see if he knows what's happening and how to stop it." She said, leaving out the part about confronting the Spirit if he was the one responsible.
The Gatekeeper opened his notebook again.
"Fluttershy is allowed to enter, but you five do not have any invitation nor have asked for permission to enter, and three of you even tried to force your-HEY!" He snapped when he realized the ponies were trying to sneak past him as he checked the list.
A flick of his tail sent a stream of wind towards the castle, turning around halfway and hitting the Bearers head on, pushing them backwards.
Twilight and Rarity lit their horns and combined their power to create a dome around the group as the Gatekeeper threw another stream at them; their shield trembled but held strong until the wind relented.
"Now none of you is entering!" The Gatekeeper declared as the unicorns dispersed the shield. "Once the Spirit is available, I'll bring the matter to him and he'll decide what to do."
"We can't afford to wait," Twilight answered as she gathered magic in her horn- before Rainbow zoomed past her. The pegasus hit the feathered reptile right in the chest, sending him backwards as she ascended, readying another charge.
But her target got up before she began descending. Inhaling deeply, the Gatekeeper blew a veritable hurricane, sending a surprised and struggling Rainbow flying away, over the horizon.
A rope slithered around him, trapping his arms and tail tightly around his chest as a scarf enveloped his muzzle. Struggling wildly against Applejack's strength and Rarity's magic, the Gatekeeper jumped to the side to avoid Twilight's spell, the blast of magic dissipating as it hit the walls of the castle.
Pushing his strength to the limit, the Gatekeeper broke free of the rope and ripped the scarf to shreds, taking deep breaths as air returned to his lungs. That distracted him for a second, long enough for Rainbow Dash to return. Slamming into him at supersonic speed, the impact released a loud and visible boom; it left the reptile buried into the ground.
"What moon hit my feathers, buddy?" he mumbled before falling unconscious.
Rarity approached him warily, glancing at the cracks around the hole and wincing at the damaged scales that filled them before turning to her huffing, feathered friend.
"A bit excessive, don't you think Rainbow?"
"He's lucky I'm not releasing a Sonic Rainboom on his tail," Rainbow muttered as she nursed a bruise in her foreleg.
"He was just doing his job," Fluttershy protested, flying over to them.
Twilight stepped between them before they could argue."I'm sorry, but we don't have time for this. We need to speak with Discord."
'And stop him if he's responsible for this.' She was careful not to voice that thought as she guided the group through the gate.
Fluttershy looked back, and quickly left her first aid kit and a muffin Pinkie had given her next to the Gatekerper, hurrying back to catch up to her friends.
