Foreword: This story was written for a shortfic prompt, requesting humorous stories of fewer than 550 words. The prompt was: Pinkie Pie engages somepony in a glowstick fight in the dark.
Light caromed out of every window in the Ponyville Town Hall, illuminating the nearby buildings and the low-hanging night fog with garish neon colors flickering red to blue to green. A pounding beat rattled the windowpanes in time with the changing colors.
Twilight Sparkle glanced again at the invitation clutched in her hoof. With a resigned shrug of her eyebrows, she took a deep breath and pushed the door open.
The music leapt through the open door like a living thing, thickening the air with its vibrations. Her eardrums cringed, but she pushed through the door and closed it tight behind her. Inside, the music was even louder. The high notes vibrated her teeth in her jaw and the low notes punched the air out of her lungs. Twilight made herself keep walking, looking around for Pinkie.
Across the room, through the strobes and colored spotlights, Twilight caught a glimpse of poofy mane, colored crimson for an instant by an errant beam of light. With sinking heart, Twilight weighed her options. All of the Town Hall's furniture had been shoved up against the rounded walls and the enormous circular floor was crowded with ponies clustering around the DJ booth in the center. To cross the room, Twilight had no choice but to go across the dance floor. She gritted her teeth and plunged in.
Several minutes later, she pulled herself from between an overly enthusiastic couple who had not seemed to notice when she got between their grinding. She wiped the sweat from her coat as she caught her breath, and wished she'd had the forethought to bring a bottle of antiseptic spray. The dancers were funky, and not in the good way.
Pinkie spotted her as she was wringing the last drops out of her mane and gave her a big, excited wave. "Twilight!" Her squeal cut effortlessly through the deafening music. She left the ponies she was talking to and joined Twilight at the edge of the dance floor. "I'm pleased as pickleberry punch that you made it, Twilight!"
Twilight couldn't help but return Pinkie's smile. Pinkie's happy face was enough to push the dance-floor funk and the pain in her ears from her mind. "I knew it was important to you, Pinkie. I wouldn't have miss— uh. What's that?"
Way up, near the high ceiling, several dozen small lights bobbed and weaved. They were green and yellow and blue and moved like drunken fireflies. Twilight's first thought was that they were pegasi, but all the pegasi at the party were dancing or hovering just above head height. She squinted, but the darkness in the high domed ceiling prevented her from seeing anything.
"Pinkie, are those decorations? What are those?"
Pinkie sighed. "Ninjas." She reached into the depths of her mane and produced two pink glowsticks. "Rave ninjas. They know I'm honor-bound to do battle with them. Back in a jiff!" A strobe flashed, and Pinkie was gone.
"...What?"