(Author's note: Since people have been asking, this story takes place during the early part of season 5 of Supernatural, and some undetermined point in season 1 of MLP:FIM.)
(Or: Welcome To My Night, Mare)
It was a dark and stormy night…
Dean Winchester stood at the rain-streaked window, gazing up at the raging sky. He shielded his eyes as a blast of lightning briefly turned night into day, accompanied by a sharp crack and a low bass boom that rattled the window in its pane. Then he looked away and pulled shut the hideous mustard-yellow and pea-green checkered curtains, silently hoping that if this had to be his last night on Earth, he wouldn't wind up spending it in this skanky hotel room.
He looked back towards the room's other occupants as another bolt of lightning caused the power to flicker, then go out. As it sputtered fitfully back on, the TV briefly flared to life, showing a grainy image of a news anchor with a yellow raincoat and umbrella, reciting an endless litany of disaster. Then the picture vanished in a burst of hissing static.
His brother Sam stood up from the edge of the rumpled, unmade bed, whacked the TV with the palm of his hand a couple of times, then gave up and switched it off. Looking over at Dean, he observed with concern, "These storms just keep getting worse, Dean. Much more of this and they'll tear the whole planet to pieces."
"That's why we need to stop it."
The brothers turned to look at the room's third occupant. He was slowly walking around the center of the room, where the beds had been pushed aside to leave an open space. As he walked, Castiel slowly poured a stream of gray ashes from a leather pouch, drawing a perfect circle on the manure-colored shag carpet. He continued without looking up, in a dryly resigned voice, "If we don't, even the Apocalypse may be a moot point."
"OK, Cas," Dean began, a bit resignedly, picking up a half-empty bottle of questionable liquor. "Why don't you explain it again. Y'know, for the slow learners in the audience."
"It's simple." Cas completed the ash circle, then tied off the bag and looked up. "These storms are not of natural origin."
"Yeah, we figured." Dean retorted. He took a drink, then gestured with his head towards the window as another blast of lightning painted the world in sickly, washed-out colors. "The green lightning was kind of a clue."
The angel gave him a disapproving look as he stepped inside the circle and set an ancient-looking wooden bowl down in the precise center. "So," he explained with visibly strained patience, "we need to journey to the origin of the disturbance."
Sam looked curious. "What do you mean? More time travel?"
"No. Time travel won't help." He poured the remains of the ashes into the bowl and stirred them with his finger, then looked up. "We'll stay at the same point in time, just move to a different reality."
Dean frowned. "Wait, how's that?"
Cas looked frustrated, glancing around the room as if seeking something. "Look at it this way."
He grabbed a stack of napkins from the dark wooden nightstand, each one emblazoned with a colorful Bloaty's Pizza Hog logo. He spread them out on the nearest bed in an approximate circle shape. "Think of these as different dimensions."
Dean looked amused. "If you say so." Then his expression darkened as Cas reached over and snatched the bottle from his hand. "Hey!"
Unperturbed, Cas held up the bottle and continued, "Now, think of this as the source of the disruption. It may be demonic, I'm not certain."
Sam raised his eyebrows. "A demon in a bottle?"
Cas exhaled heavily. "Try not to be so literal."
He held the bottle over the napkins. "Now, this entity is centered in a single reality. But the effects of its actions spill over into others, including our own. Like this." With that, he tilted the bottle and began to pour its contents in the center of the napkins, soaking their edges as the brownish liquid spread across the sheets.
"HEY!" Dean protested even louder, and rushed over to grab the now-mostly-empty bottle back from Cas. "Quit using my stuff for your visual aids, dammit!"
"Yeah, Cas," Sam observed, deadpan. "Dean paid almost five dollars for that booze."
Dean glowered at him. "SHUT up."
Castiel looked exasperated. "Do you understand? If it is a demon that's causing all this, we can't stop it from here. We need to travel to the dimension where it's strongest."
He tilted his head slightly, his gaze unfocused, as if he were listening to something human ears couldn't hear. "And we need to act quickly. If these storms continue unchecked, they'll rip this world apart. Along with any other worlds affected by this evil."
Dean took a swig of what was left of his drink as Cas crouched beside the wooden bowl again and dropped the empty leather bag inside it. "So," Dean said, wiping his mouth with the back of his hand, "when we do this dimensional-travel gig, we bring along every anti-hellbitch thing we've got, right? Demon knife, holy water, the whole deal?"
Cas shook his head as he stood up. "No. You can't bring any physical objects with you."
Dean's sarcasm would've moved mountains. "Oh, terrific."
Sam blinked in alarm. "Wait, no physical objects at all?" He glanced down at himself, tugged at his shirt, then looked up again. "So will this be like a, you know…Terminator thing?"
Cas looked pained. "I never understand what you're talking about." Then he glanced down at the bowl. "I need one more thing." With that, he vanished with a familiar wing-flapping sound.
Dean sighed. "I hate when he does that." Lifting the bottle for another drink, he turned around, and nearly ran into Cas coming the other way.
"Excuse me." Cas moved around him, then crouched beside the bowl.
Dean glared at him, then looked at Sam in exasperation. "And I really hate it when he does that!" Sam could only give a resigned shrug.
Then Dean happened to notice the glittering, marble-sized objects Cas was placing into the bowl one by one. Blinking once, Dean asked, "Wait. Are those diamonds?"
Blinking again, he demanded, "As in real diamonds?"
Cas looked impatient, clearly not understanding why the subject was still under discussion. "Yes."
Dean let out a low whistle. "Damn." He shook his head. "Any one of those babies could probably buy us a house."
"Several houses, most likely."
Dean said no more, but silently consoled himself by tilting his bottle back and guzzling the last of its contents. Sam, who'd been watching without comment, finally asked as if he didn't really want to know the answer: "Cas…where exactly did you get those?"
He replied without looking up, "From a bank vault in Phoenix."
Dean sprayed his drink halfway across the room. Sam sputtered, "You can't just-!"
Cas interrupted, "Sam, don't you think there's a certain-" he made air quotes,"-'greater good' involved here?" Dean was too busy coughing violently to add anything as Cas insisted, "The ritual must be performed now. We won't get another chance at this. Are you two coming, or not?"
Dean fought down his coughs and spoke in a raspy voice. "Fine." He tossed the empty bottle in the trash, then stepped inside the circle of ashes. "But when we get back, you and me are gonna have a serious talk about finances."
Joining him inside the circle, Sam shot his brother a warning glare. "Don't even think about it."
Dean affected a pouty face. "Spoilsport."
Cas gestured towards the floor. "You should probably be seated."
They complied, sitting cross-legged on the floor across from him as he raised the bowl in his hands. The contents of the bowl made a rattling noise as he swirled it three times, then set it down again. Dean joked, "We're not gonna have a sing-along, are we?" However, he received no response other than an exasperated eye-roll from Sam.
Cas looked over his handiwork once more, then nodded in satisfaction. "Everything is ready." He glanced over at them. "You won't be able to remain in your human bodies, I'm afraid."
Dean's jaw dropped open with an incoherent "hwha?" sound as Sam demanded in a voice at least two octaves higher than normal, "Wait, WHAT?"
"You should prepare yourselves." Cas raised his hand palm-down over the bowl, closing his eyes.
A brilliant white glow consumed the room as, in overlapping voices, Sam protested "Whoa, wait, hang on," and Dean yelled, "Cas, you son of a-"
. . .