Behold Your Tuberous Savior
Princess Luna stepped forward. "Tirek is set on possessing alicorn magic. When he comes for us, we cannot have what he is looking for."
Twilight hesitated for less than a second before replying, "I'm more than willing to do my part and give up my magic."
"You misunderstand," Luna cut in. "Our magic cannot just disappear into thin air. Somepony must keep it safe."
"My sister is correct," Celestia added, pulling an ancient-looking box from behind her throne. "If we are to keep Tirek from obtaining our magic, then we must transfer our magic where he cannot find it. We must transfer it to..." Celestia opened the box. "This potato."
"Huh?" Twilight said in surprise, leaning in and looking into the box. Sure enough, there was a potato resting on the pillow within.
Celestia continued, "Tirek will not expect to find our magic hidden inside this moldy potato, and Equestria will remain safe from his tyranny."
Twilight nudged the potato, feeling the fuzz and hairs tickle her hoof. She recoiled suddenly as the potato shuddered and wiggled on the pillow. "Celestia, is this thing...."
Princess Celestia nodded slowly. "It is. Though most potatoes die shortly after being harvested, this one has become so overgrown with fungus that most of its mass is indeed alive. Magic must have a living host to be properly stored, else it spoils over time."
Twilight looked long and hard at Celestia's stony face, trying to figure out whether she was joking or not. The other princesses weren't laughing and nopony was saying, "Gotcha!"
"Are you sure this is the best thing to do?" Twilight asked. "Couldn't we transfer the magic to, oh, I don't know, me maybe?"
Celestia chuckled slightly, turning away from Twilight. "Oh, Twilight, I never tire of your sense of humor." She turned back after a moment. "Are you ready?"
Twilight looked at the other princesses, desperately hoping that one of them would start cracking up, but none did. She sighed. "Yes. If it means keeping Equestria safe, I'll give up my magic," she turned to the tuber in the box, "and put it in this potato."
The four princesses gathered around the ancient box. They poured their magic out, forming a massive ball of energy that almost reached the ceiling. The magic was then channeled down into the potato, which didn't react in any way, for it was a potato. When they were done, all four princesses slumped to the floor, drained of all their power. Twilight blacked out.
Twilight came to after an unknown amount of time had passed, and got to her hooves. Her legs were as oatmeal beneath her, and she was barely able to stay standing. Her gaze drifted around the room, taking in the other alicorns. All were still incapacitated. Slowly, her eyes moved to the floor. There, a few feet from her shaking hooves, was the box. The potato had not gone anywhere, for it was a potato.
"Alright," Twilight croaked out as the other princesses began to stir, "we have to hide this potato away someplace that Tirek will never find—"
The throne room doors exploded inward, and Tirek stomped into the room, the floor quaking with each step his monumental frame took.
"Aw, crap," Twilight muttered.
Tirek pulled Princess Celestia up to his open mouth and inhaled, but no magic came to him. "What have you done?" he growled. Celestia just smirked at him, and he moved on to Luna. Finding no success there, he turned to Cadence and finally Twilight, but there was no magic to steal. "Where is your magic?!" Tirek screamed, doing a frighteningly-accurate impression of Iron Will.
Tirek scanned the room, fuming with indignant rage. Finding nothing, he crossed his arms and took a seat in Celestia's throne. He smirked after a moment as he looked down at the alicorns. "Getting rid of your magic so that I cannot take it from you? That was your plan?" Tirek waited a moment, but nopony gave him a response. "How does it feel knowing that every pegasus, unicorn, and—ow! Wha?"
Twilight gasped as the potato hovered in front of Tirek's puzzled face. It glowed with magic, and the potato had sprouted a little horn and a pair of moldy wings. It shot forward suddenly, punching the beast right in the mouth.
Tirek spat, wiping his lips clean of fungus. "What in Equestria—"
But the potato didn't let him finish. Instead, it pounded his face and body, slamming itself into him from every angle. The chest, the gut, the eye, the crotch, the foot, the crotch, the other gut, the crotch—no part of his beastly form was spared from the barrage of tuberous blows. Tirek began to cry as his bruised body crumpled to the floor, the potato refusing to halt the beating that it was unleashing on him.
Tirek turned his blackened eyes to the four princesses. "Please, make it stop!" But they only stood there, all but Twilight simply staring with cold eyes. Twilight's mouth was hanging open, her violet eyes wide, but she didn't move to stop the potato as it battered the monster.
After another three hours, Tirek finally stopped weeping. The potato continued to beat him for a few more minutes, just to be sure, but then it slid back into the box. Twilight finally closed her dry mouth and shook her head, trying to comprehend what she'd just witnessed.
Princess Cadence stepped over to Tirek's body, cautiously poking him with a hoof. He didn't react, and Cadence turned to the others. "I think he's dead."
"Huzzah!" Princess Luna shouted.
Celestia simply nodded sagely, as though everything were going exactly as planned.
"Um," Twilight started, "what just...."
The potato rose up from its box suddenly, and magic spewed forth from its moldy surface. The ball of energy formed again, and then channeled itself into the four alicorns. Once it was finished, the normal-looking (albeit moldy) potato fell back into the box. Celestia closed the lid carefully, and slid it back into its hiding spot behind her throne.
"Well, that certainly was different," Twilight commented. "I can't say I've ever seen that before."
"Hey, if anypony asks," Cadence piped up, "can we say we just beat him senseless?"
Celestia nodded again. "I think that would be best, yes."
"Agreed," Luna said. "I do not think that Equestria is quite ready to know about something like this."
Twilight nodded numbly. "I sure wasn't."
