"No..." Celestia stammered, backing away as a cat wandered into the throne room. "No, no! Get away!"
The cat approached.
"Away, you fiend!" Celestia pulled a longsword from behind her throne and pointed it at the cat. "Back off!"
The cat approached. Faster.
Celestia screamed in terror as the cat hopped onto the throne that she'd just vacated moments prior in her act of drawing the sword.
"What have you done?"
The cat meowed. It batted at one of the armrests (forelegrests???), causing a small button to emerge.
"No, no do not press that button."
And of course the cat, being what it was, pressed the button. Sirens immediately blared all around as the lights dimmed to a deep crimson. Celestia continued to scream and scold the cat, but her efforts were for nothing. It'd already been done.
"What have you done..." Celestia pulled back, her voice weaker than before. "No..."
The cat continued to sit on the throne, which in reality was a random chair that Celestia had stolen from her elementary school many, many years ago. Heavily modified since then, though.
The alarms continued to rattle Celestia's skull.
Slowly, the room began to tremble. A deep, grinding mechanical noise reverberated through the air as the trembling shifted into a violent rocking.
Celestia crouched low to the ground, her eyes locked with the cat's. "It's too late now. Brace yourself."
Twilight's jaw dropped as Canterlot Castle quite literally grew legs and walked away.
"So that's what she meant when she said she had a mobile home."
The ICBM crashed down in the center of Ponyville seconds later.