It seemed like the entire mountain was rocking. At least from Twilight’s perspective as she stood in the palace gardens. Around her lights were flashing, music was booming, and ponies were dancing. The famous musician, DJ Pon-3 was spinning records, laying down the sound of the party, but its true heart was the bouncing pink pony who had planned and implemented the city-wide celebration, who seemed to be absolutely everywhere at once.
She popped up behind Twilight just as she thought that, nearly making her drop her cup of punch. "Hey Twi! How’s the punch?"
"Oh, hey there Pinkie," shouted Twilight over the music. "It’s good!"
"Yay! It didn’t taste funny?"
"No, not at all." Twilight suddenly regarded her cup with suspicion. "Why, what’s in it?"
"Nothing! Just a new recipe, that’s all. The cake is a new recipe too." Pinkie grinned hugely, then bounced off again.
Twilight looked after her. Something had seemed... off about that grin. Pinkie grinned all the time, yes, and her grins were usually pretty manic, yes, but that one had been even more manic than normal. There had been an edge of something disturbing about it.
Twilight wandered through the party, looking for Pinkie. She wanted to make sure that everything was all right. A moment ago Pinkie had seemed to be everywhere, but now that Twilight was looking for her, she couldn’t find any sign of her. "Figures," she muttered to herself as she searched. All around her ponies danced and played and sang, but none of them were the pink pony she needed to find.
She walked a little faster. Pinkie had to be here somewhere. The music, which a moment ago had lifted Twilight's spirits, was now hurting her ears. It seemed like nothing more than noise, and it made her head throb with pain in time to the beat. She scowled and kept searching, but still found no sign of Pinkie.
Twilight started to run. Threads of panic worked their way around her. She couldn’t even say why, she only knew that something was wrong and she had to find Pinkie, soon. She blundered through the crowd, shouldering ponies out of the way as she went. Still no sign of Pinkie. Twilight was finally forced to take wing. She soared up above the party, barely managing to concentrate on flying and scanning the ground below her at the same time. She still couldn’t find Pinkie, but she did see a large, white form amid the crowd below.
She swooped down and managed to land next to Princess Celestia without crashing. "Celestia! Have you seen Pinkie Pie?"
Celestia turned to her, looking down at Twilight with a reassuring smile. "Not recently. Why, is something wrong, Twilight?"
Twilight looked up, about to say, "Probably not," but the words died on her lips. Celestia’s eyes shone with a faint pink glow.
Suddenly the music halted, leaving an echoing silence. The shouting of playing ponies died away too, leaving only a low murmur of confusion in its wake.
"Suprise!" The voice rang out loudly over the crowd. It was almost deafening, in fact. Twilight turned towards it, to see Pinkie Pie, standing on top of the dessert table, one hind hoof planted on each of the towering cakes there. She reared up above them, her form impossibly tall. Her mane and tail swirled around her, and a pink numbus seemed to radiate faintly from her.
"Pinkie! What are you doing?" shouted Twilight.
"I think it’s time for the party to last forever!" said Pinkie.
"No, you can’t just do this!" said Twilight. Her eyes narrowed in determination. Even though it was her friend, she wasn’t just going to let Pinkie get away with this.
"I can just do this, silly filly," said Pinkie, grinning. It was that disturbing grin again, the one that was just a little bit too wide, even for Pinkie. The pink glow around her brightened. Twilight frowned. She felt... like dancing. The music started up again and Twilight’s feet started moving. She twitched and jerked, dancing with no regard to the beat. All around her, other ponies were dancing too, though their hooves kept perfect time. Their eyes glowed pink, the glow pulsing in time with the music.
Twilight couldn’t quite match the pulse, no matter how she tried. She wanted to. She wanted to be part of the party. That was all that a pony should want, wasn’t it? Ponies partied, that was what ponies did. But Twilight couldn’t, no matter how hard she tried. Frustration filled her. What kind of pony was she, if she couldn’t dance? All the other ponies could dance, what was wrong with her? What was wrong...
No, it wasn’t her that was wrong, was it? It was the dancing! It was the party! Twilight pulled free of the pink haze. She spread her wings and rocketed up above the dancing crowd. Below she once more found the large, white shape of Celestia. Luna’s only slightly smaller dark form dance beside her. Feeling relief, Twilight flew down to them. She just had to break them free and they could fix Pinkie. Everything would be alright.
She landed next to Celestia. "Princess! Princess Celestia! Wake up! Snap out of it!"
Celestia turned to her. "Why aren’t you dancing, Twilight?"
"Because this isn’t right. Life isn’t supposed to be nothing but a party, and parties aren’t supposed to last forever. Come on Princess..."
"The fun shall last forever, Twilight," said Luna, coming up beside Twilight. She was suddenly bracketed between the two larger alicorns. She looked between them, feeling her stomach sink. This wasn’t going well at all.
"Please, Princess," said Twilight, but was cut off as Celestia pushed a bite of cake into her’s mouth.
"Eat the cake, Twilight."
"Eat it, and give in to the party," said Luna.
Twilight tried to spit the sugary mouthful out, but Celestia’s magic was clamped around her muzzle, preventing her. The sweetness coated her tongue, and from there it spread through her whole being. It made her happy. She felt a sudden urge to dance, and began to move her hooves. They moved, now, in time with the music. She swallowed the bite of cake.
It seemed like the whole mountain was rocking. All the ponies of Canterlot danced to the beat of the music that the DJ spun at Pinkie’s request. The Pink Party Nightmare bounced among her subjects, laughing and playing all her favorite games, as the music spread further and further across the land, until all ponies knew the joy of the party that would last forever.