“Dang it,” the crystal guard said as he descended the stairs into the palace's wine cellar, “who needs a bottle of wine at this time of night? And can't just get it themselves? Frigging chefs.”
Continuing to grumble, he stormed into the room proper, his annoyance not quite enough to overwhelm his care about where he was putting his spear – he was no epicurean, but he knew just how valuable many of the bottles in this basement were.
It was because of this that he wasn't looking directly in front of him for a moment and almost walked right into a small wine rack situated right in the middle of the room. Fortunately, his peripheral vision was sharp enough that he noticed it just before he would have hit it, sending his head whipping towards it and his hooves hard into the floor, locking him in place.
“Gah!” he exclaimed, backing up a little and walking around the obtrusive installation, careful not to touch the rack or the probably-valuable bottles on it. “Stupid place to put that!”
Once past it, he continued to the back of the room, where the stores of the ordinary wine were kept. He quickly opened the bag he'd been given and shoved three bottles in. He'd only been asked to fetch one, but he knew how chefs worked and he wasn't about to come all the way back down here just because they'd realized they needed more.
Snorting at the waste of his time, he carefully stepped around the central rack again before heading up the stairs and out of sight.
Once the sound of the door to the cellar opening and closing had faded, the wine rack breathed a sigh of relief.
“That was too close,” it muttered as its form began to wobble and distort. In a few seconds, it faded into nothingness, revealing a small filly standing where the image had been, her head covered by a domed crystal helmet.
The filly smiled as she too walked to the back of the room, taking a key out of her small saddlebags.
“Good thing the guards are so stupid,” she continued murmuring as she gently thrust the key into a blank section of wall. “Everypony knows that's not how a wine cellar's laid out.”
She fiddled with the key for a short while, scraping it around the wall apparently in search of a keyhole, even though there wasn't one visible.
After a moment, however, it fell through a solid-looking section of the wall, clicking as it shifted the tumblers in the hidden keyhole and turned.
Pushing forward, the filly's hoof disappeared through the wall as well, soon followed by the rest of her.
Over the near-imperceptible sound of the pristine door hinges closing, the filly's muttering could just about be heard through the illusion.
“It doesn't matter – I'll be done soon anyway. Soon, Sombra's secret will be mine!”