Star Swirl paced back and forth in front of the two rapscallions, throwing glares and snorts, and reassuring himself that disaster had been averted, and his hat was safely where it belonged. "Equestria is safe again."

Luna gurgled, eyes and cheeks bulging.

“No thanks to you two!” He barked.

Celestia met his eyes, back straight, neck firm, and chin lifted. She was the picture of regal poise, aside from that twitchy-lipped, half-hidden smile giving away her tacit enjoyment of such a low trick.

Luna had her hooves braced over her muzzle as she shook, and her cheeks bulged near to bursting when he leveled a raised eyebrow at her, then Celestia. “Do you think I am joking?”

Their heads bobbled like ducks on a wave-tossed pond, eyes wide. Well, he would make them quack to a different tune.

“Young fillies..." It could have been a curse. “There are things in this world that would turn your mind inside out from sheer terror, things ponies cannot comprehend!”

Luna’s cheeks quivered with the effort of holding in what was surely a horrified scream. And would have been, had her eyes not twinkled so merrily.

"I was terrified!" Celestia's eyes bulged.

Luna choked, hooves clamping tighter.

Yelling at them wasn’t going to make them see reason, if reason was in their young minds at all. Nor would scaring them, as they seemed immune to even the idea of fear. He watched them, not quite teenaged fillies so certain of their own destinies emblazoned on their flanks. As he had, once.

“Celestia, Luna. Come close. I want you to hear every word, as you did when I taught you teleportation, and how dangerous it can be. Understand?"

"So, no more dumplings on the ceiling?” Celestia asked.

He shook his head. “Long ago, a great evil was unleashed upon the land, an evil so monstrous that nopony could rise in its presence, for it sucked the air from their lungs and left them shaking in terror.”

Even Luna was managing to look more like a pony with an overfull mouth than a chipmunk in bad need of her tree, until Celestia leaned over to whisper something to Luna, a foul lie, no doubt, as both fillies burst into hurriedly quenched giggles.

He stood again, reached to touch the brim of his hat, and paced to the window. Outside, the sun was shining, birds were chirping, and the gardeners chattered on about idle gossip from the kitchens.

“Do you know what evil was summoned to Equestria?”

“No sir, Mr. Star Swirl.”

“Star Swirl the Bearded, young one.” He flipped his beard back and forth, reveling in the soft, flowing silver locks, and considered. “I was not always called such, however.” He turned and lifted a hoof to forestall the incoming flood of questions surely bubbling up in their minds. “I will tell all.”

He turned to the chalkboard, frowning.

“How did you defeat it?” Luna asked.

"He put on a hat!" Celestia giggled.

“No.” He sighed just as his hat flew off.

The residue of magic was already fading into an indistinct cloud when he spun, and two innocent-as-foals faces smiled up at him.

“Mr. Bearded.” Celestia squinted. “Is that you? I can’t see past the glare.”

Luna snorted, clamping a hoof over her muzzle.

Celestia smiled sweetly, but she couldn't hide that merry set to her ears, nor the twinkle in her eyes.

He glared at both of them and settled his hat back on his head, cutting out the bright light. Harrumphing at her smile, and fighting an answering one, he feigned a turn, and caught Luna’s horn glowing blue just as his hat winked out of existence.

Outside, a gardener shouted and poked her head in the window, but her breath caught in a gasp and she fell back, giggling.

Star Swirl shook his head. It would be a week -- a month! -- before castle gossip turned away from his mirror-finish pate.

The suppressed giggles from both fillies erupted into gales of laughter, and they all collapsed in heaps, gasping for breath.

“Why did I think you girls would take this seriously? How would you deal with an immortal spirit that cursed your mane to grow from your chin! Or plucks your tails from your behinds!” He tweaked their tails for good measure.

“Sun power!” Celestia tackled his forelegs.

“Moon power!” Luna grappled his hindlegs.

He had to admit, when he could breath again, and disentangled himself, that tickling was very effective.