"How did you figure out it was me, sister?"
"Well, the tip of your horn had poked a hole in the sheet and about an inch of it was showing. You used your own sheets, which have your name and the phases of the moon repeating along the edges. But mostly? Our manes are ethereal energy, which isn't blocked by thin silk. I could see your mane and tail the whole time."
"Oh drat." Princess Luna took off her amazing spirit disguise. "I knew I should have used one of your sheets. Your name and the suns would have confused you into believing it was yourself!"
"I don't think that would have..." Celestia paused in thought. "Okay, that might have worked. I'm thinking about teaching Twilight time travel magic soon."
"What about my perfect plan to throw you off the scent with that perfect doppelganger in my room?"
"You mean that's what Cadance was doing in your bedroom with the lights out and speaking in that atrocious caricature of a bat pony accent? She tripped over something in the dark. In the dark!" Celestia paused to think about it all. "However, she did attempt to disguise her voice without needing somepony to point it out. So I have to say it was the best part of your entire plan, sister."
The two sat in comfortable silence for a few countless minutes.
"You want a plain headstone to mark your passing?" Luna relaxed by her sister's side, their wings draped over each other. "We are doomed to have elaborate monuments for our resting places, dear sister."
"I know. Their ambitions have only gotten worse while you were gone." Celestia rested her head against Luna's neck and closed her eyes. "They keep trying to build a monument for me in secret since I said I don't want one. The last attempt managed to last eight months before I found out about it. They hadn't even finished clearing and leveling out the ground at that point."
"Did you find plans for what they intended to build?" Luna's wing gave her sister a warm squeeze.
"They were planning on building a gleaming gold pyramid the size of this entire mountain with a statue of me on it the size of Canterlot."
"That does seem excessive." Luna shifted position slightly so she could nuzzle her sister's cheek. "Even the ancient crystal architects did not dream so big."
"Thank you for all of this, dear sister." Celestia nuzzled back. "It might not have gone as you wanted, but it was just what I needed."
"If you are feeling better, that's the most important thing. The rest, well, I will take it as a lesson to spend more than a half-hour to prepare a prank. Should we go back to the palace now?"
"Not yet. There's another play you should know about. It's called A Hearth's Warming Eve Story. I'm sure Ponyville won't mind helping us have a bit of fun with Twilight Sparkle tomorrow."
Both princesses giggled. They would enjoy spreading the fun, but later. For now it was wonderful to finally spend a Hearth's Warming Eve with family once again.