Courage immediately recognized the item that Luna pulled out of the closet. It was a battery powered vacuum. Cordless, of course, as outlets were nearly unheard of in Equestrian society. A very large one at that, about double the size of the standard shopvac. He could only think of one use for it in such a time as this, and looked up at Luna with surprise at her ingenuity, but also fear at the thought of what might happen if it didn't work.
"You sure about this?" He asked.
Luna didn't immediately understand him as she had a moment ago, but would recognized the slight tilt of his head as the universal symbol for confusion. "If fog needs to be contained, what better way to contain it than with a suction mechanism?" She asked. Going with Courage to the end of the hallway she looked down over the balcony to the lowest floor in the entryway. The fog had rolled in through the doors, and there was no sign of the patrolling guards which Courage had seen only minutes earlier. He shivered at the implication, knowing very well they were still down there... somewhere.
Until the fog could be dispatched, they were stuck up here. It was still active, bubbling and foaming violently. Luna looked down, frowned and her horn sparked to life. Brilliant purple aura shot into the vacuum with such force that Luna herself was nearly thrown backwards. It blazed into the tool as a blasting pillar of violet light, Luna cringing all the while as if she were significantly uncomfortable.
When the light finally faded from her horn, the alicorn panted heavily, her heart racing. "I've charged up the vacuum with moonbeams," she said. "Moonbeam is a very pure light, and hopefully should be able to counteract the dark forces, otherwise we'd only be sucking up fog without any real progress. Give it a try, pup." She smiled knowingly.
Courage nodded, and picked up the nozzle of the machine. He flicked it on with his paw, giving a startled jump as the vacuum roared to life. The nozzle vibrated and swung around with such force that poor Courage was tossed around in the air in all sorts of random directions as the hose danced wildly in the air, with the canine clinging to it in the hopes he wouldn't be thrown into the fog and consumed.
Luna acted quickly, and took hold of it with her magic, with Courage sliding down onto her back. "Perhaps I should do this part," she said gently, and stepped forward. The hose found the fog almost instantly once it was contained and aimed, and the fog resisted only for a moment before being pulled into the nozzle.
Courage yelped and pointed as a fogpony rose up out of the mist and screeched at them, but Luna aimed her weapon at it. The hose pulled the fog away from the monster with such power that the fogpony screeched even louder, bright rays of moonbeam shooting from its body in all directions. The fogpony gave one final screech before there was the sound of shattering glass, and the mist removed itself from a very disoriented looking guard, who was blinking slowly as if waking from a very deep sleep.
"You alright, there, Cornelius?" Luna called, and the guard slurred some sort of acknowledgement.
"How did you know that would work?" Courage asked, peering over her shoulder.
"I didn't, but I saw something similar in one of my games," Luna said. "Granted, it was about this writer pony searching for his missing mare with only a torch to fend off the darkness, but this isn't all that different," she said. "Come now, there's much to do!"
Progress was mind numbingly slow, and the hours wore on as they pushed their way out of the castle and down the street, revitalizing one fogpony after another. There were guards, and thankful Canterlot residents, but no sign of the mares whom Courage had come here with. They made their way down the street just far enough for Courage to see where the Apothecary stood, and leaped off Luna's back onto a safe patch of ground where they'd already sucked up the fog.
"Little dog, wait!" Luna called, but Courage ignored her. He ran to the front of the shop, yanking on the front door with relentless determination; but it was locked. Courage kicked the front door with such force that he hurt himself, but was no closer to getting in. Dark laughter came from above him, and he looked up to see Katz grinning at him triumphantly from the giant spinning cauldron that advertised the store.
"I'll admit, I'm impressed you made it this far, Courage!" He admitted. "But you'll never win! My fog is everywhere, and not even you can stop it all!"
Courage pouted, trying to scramble up the front of the store, but continually slid back down. He growled in anger, before spying the yo yo dangling from the tree that he'd used previously. He ran towards Luna, leapfrogging off her back onto the trunk of the tree, almost immediately sliding downwards towards where several fogponies were waiting. He yelped and scrambled back up, grabbing the toy and unwinding it from the branches.
Katz was too busy laughing and taunting him to much follow this, so Courage had time to twirl the toy over his head like a lasso, before throwing it. His aim was true, and the string first wound around Katz' ankles before spiraling up his legs. Katz shrieked with annoyance and reached down to unbind himself, losing his balance in the spinning cauldron.
He fell, then, with a terrifying scream, right off the top of the building into the purple haze below, where numerous fogponies were eagerly waiting to catch him.
"No! NO!" He screamed, struggling to escape their grasping hooves and gaping jaws. "Don't you know who I am?! I'm Katz, you idiots! Katz! RELEASE me, you brainless sacks of-" Hi screams were cut off as the fogponies pounced on him, and although both Luna and Courage looked away, his screams still echoed through their minds.
Almost immediately... the fog began to lift. It sizzled, steamed, smoked, and evaporated, spiraling towards the dark sky in great plumes, leaving behind incredibly confused, otherwise healthy ponies behind. Little by little, the streets began to clear, and things began to return to normal.
"Yes!" Courage exclaimed, then looked down to where Katz had fallen. The fog had lifted, and there was no sign of him. Nor was there any sign of the three girls whom he'd befriended.