The next morning, at the appointed time, Haystacks knocked on Rainbow Dash's door. After waiting a moment and receiving no response, he knocked louder.
"Huhhhg. Coming!" came back a muffled response. Haystacks raised an eyebrow. Did she usually sleep late? It was true that he did, but then, he was generally up most of the night working and then slept during the day.
"Ti-haaa-me already?" Rainbow Dash said with a yawn as she opened the door. Her mane was dissheveled, and for some reason she was wearing a robe.
"Yes?" Haystacks said, making it a question. "I could come back in a little bit, if you need some time."
"No, I'll just grab an oat bar for breakfast. Want one?" Rainbow Dash said, turning back into her house. Haystacks shook his head, then realized that she could not see that.
"No, I already ate. Thanks, though," he said. "Actually, this would be a better place to start today. Before any more tests, I have some special training."
Rainbow Dash perked up a little at this, turning back to face him. "Is it some sort of super-secret training that the Wonderbolts use?" she said excitedly.
"Um... no," he said, dropping his gaze a bit on the last word, "At least not as far as I know. For any maneuver other than pure speed, this would probably hurt more than help. But I've wraked my brains and can't come up with any better ideas."
"Wow, mysterious," Raindow Dash said, before taking a bite out of the oat bar she had found. "Feel like sharing with the class?" she said around a mouthful of food.
"Heh," Haystacks chuckled with a smirk, "You know, I wasn't intended to be mysterious, but since you brought it up, I think I'll build it up a bit more."
Rainbow Dash rolled her eyes in response. "Oh, come on."
"Now," Haystack said, starting to pace as he slipped into 'lecture mode', "This is a trick my uncle taught me when I was a foal. I'll tell you what he told me: this can be dangerous, so don't do it without a spotter."
He looked directly at Rainbow Dash as he paused his pacing. "Speaking of which, that's your job," he said.
"Fine, whatever. Get to the point!" she said impatiently.
"Alright," Haystacks said.
The green pegasus took a deep breath, closed his eyes, and tucked his wings close. Slowly, almost imperceptibly at first, he sank into the clouds. Rainbow Dash's eyes went wide as her temporary trainer sank out of sight entirely.
"Woah, what?!" she exclaimed, rushing over to where he had been. She found no hole in the cloud.
"Guess you'd have made a better spotter had I said what to expect," Haystacks said from behind her. She spun around to find him flapping his wings in a hover.
"Wow! That...was...awesome!" Rainbow Dash said, "How did you even do that? I mean, busting through clouds is easy enough, but to just sink in without leaving a mark?"
Haystacks smirked as he landed. "That was more or less my reaction when my uncle showed me," he said, "Now, before I explain it, do you have a guess?"
"Huh? No! That's why I'm asking you!" Rainbow Dash said.
Haystacks started to sigh, then stifled it. He did not want Dash to think he was frustrated with her. It was his own difficulties with teaching that were the issue.
"Alright, let's walk through this," he said. "What happens when a unicorn or earth pony tries to stand on a cloud?"
"They fall through, obviously," Rainbow Dash said, "Everypony knows that."
"Right, but why don't we?" he asked.
"Because we're pegasi?"
Haystacks rubbed his chin. "Well, yes, but not what I was getting at. You know how sometimes Celestia will provide a spell so that earth ponies and unicorns can visit cloudsdale for big events?"
"Yeah, that sounds familiar," Rainbow Dash said. She had only the vaguest of memories of such an event from fillyhood.
"Well," Haystacks continued, "That spell is essentially replicating the innate magic we pegasi possess. It's the same magic that lets us manipulate the weather."
He paused for just a second and on getting no reaction, pressed on.
"It's something we do mostly without thinking about it. Cloud busting, though, takes a little bit of learning. After trusting clouds as impassable objects for most of our early lives, we have to see them as breakable to properly disperse them." Haystacks noticed here that he was starting to lose her attention. In response, he let his eyes unfocus and sank just a few inches into the cloud before his eyes snapped back into focus. This caught her attention.
"You see, just then, I managed to see the cloud kinda like I would for cloud busting: as something malleable. It's like a mudpit, if you've ever been in one of those. You can move through it, but only sluggishly, as the stuff resists your movement," he said. "My uncle described it like swimming through mollassas. By seeing it as a viscous fluid... errr, like honey," he made a substitution on seeing her look of incomprehension, "You can sink through the cloud. It then will flow back together as you pass through, so you don't leave a mark!" He was starting to hit his groove now and was showing his excitement at the phenomenon. He grinned at Rainbow Dash as he stepped back up to normal cloud level.
"In other words," he said, "By focusing, it's possible to bypass our normal subconscious restrictions on how we use our magic, and use it in other ways! If you can manage that, then you can apply the same principle to flying, and hopefully that will give you the extra boost to cross the magic... or if you prefer, Rainboom, barrier."
"Right, cool, whatever," Rainbow Dash said impatiently, "Why the spotter, though?"
"Weeeell," Haystacks said, prevaricating a bit, "When first learning this, the most common problems is falling through too fast. You're a good enough flier that I don't think that's an issue. Other possible problems include focusing so much on the trick that you don't notice that you've fallen through, and getting stuck in the middle of the cloud."
"Stuck?!" Rainbow Dash said with some trepidation.
"Yeah, but don't worry, it's easy enough for somepony else to pull you out," he said. "Ready to give it a try?"
"Finally!" Rainbow Dash said, "Alright, here I go!"
Rainbow Dash closed her eyes and folded her wings tight, as she had seen Haystacks do. Then... nothing happened. Clearly there was something else she was supposed to do. She screwed her eyes shut tighter and gritted her teeth. Haystacks, watching, shook his head.
"No no, it's not just a matter of generic effort. To start with, focus on how the cloud feels under your hoofs," he said. Rainbow Dash opened her eyes.
"Huh? What's that supposed to mean?" she asked.
Haystacks blinked. "I... don't know how else to say it," he said, "Compare how a cloud you're standing on feels and how a cloud you're busting through feels. Then you just sort of... subsittute the latter for the former."
Rainbow Dash cocked her head sideways in confusion. Haystacks sighed.
"Sorry, I'm not very good at describing it. Maybe... ok, yeah. Let's gather up some other clouds," he said.
Finally, something she understood. "On it!" Rainbow Dash said, dashing off into the air. In about ten seconds flat, she had pushed five small clouds around where Haystacks was standing. He clucked his tongue appreciatively.
"Nice," he said, "Ok, so to start with, just fly through one."
"Piece of cake," she said. She casually swooped up and flew down at speed, dispersing one of the small clouds and stopping on a dime to land on the cloud that was her yard.
"Ok," Haystacks said, nodding, "Now, set one over another. This time, fly down hind-legs first, like you're dropping into a kick."
Rainbow Dash quickly arranged the clouds and kicked down through them.
"Errr, I wasn't finished," Haystacks said.
"Eh heh... oops," Rainbow Dash said sheepishly, rubbing the back of her head with her forehoof.
"Ahem. Yes," Haystacks said, fake-coughing and putting his forehoof in front of his mouth. "As I was saying, fly down like you just did, but only through the top cloud. Without slowing down like you normally would, land on the second cloud. You might want to bounce off of it, actually, or you might hurt your hoof. Assuming you do it right, anyway."
"Huh," Rainbow Dash said, "Doesn't sound too hard."
She repeated her previous action, but this time slowed down drastically just before hitting the second cloud. Not enough, however, as it started to drift apart. She hastily gathered it back together. Haystacks smirked.
"Tricky, isn't it? And don't think I didn't notice you slow down there. Try just bouncing on the cloud first, while I grab some more clouds," Haystacks said.
For the next few hours, Rainbow Dash tried to learn the 'cloud phasing' technique, as Haystacks called it. She managed to fly through one cloud and bounce off the second after only a few tries. Haystacks had her repeated it to be sure she could do so consistently. The next stage involved making the clouds thinner and closer together. This repeated incrementally for a good while, as it took a few trials to first find where she started having trouble again, then several more runs with the same parameters for her to get the hang of it at that point. Rainbow Dash was used to repetitive training, but after a few hours she became to become visibly frustrated.
"Ok, it's about time to break for lunch," Haystacks said, "But first, try something closer to the end result just once. Fly slowly at your patio here, then land on it and slowly sink through it. Think you can manage that?"
"Finally!" Rainbow Dash said, "Here goes nothing!"
She tried the trick this way, flying at low speed into her cloud patio. She did start to sink through it, but stopped about knee-deep. She pulled at her hooves, but they seemed to be stuck.
"Ah!" she exclaimed, panic rising, "I can't get loose!"
Haystacks winced. "Yeah, that'll happen when you're learning," he said, "Hold on..."
Haystacks flew over and under the lip of the cloud. Rainbow Dash stopped struggling and blinked, wondering what was going on. Suddenly, she felt something warm beneath her hooves, sharply contrasting the cold cloud, and she began to rise out of it. Once her hooves were free, she flew up to get a better look. Haystacks slowly rose up out of the cloud and, once free, shook off the few clinging water droplets. He had flown under her to push her up from below.
"See? Spotter," he said with a smile, "Now, lunch break!"
They talked over lunch. Rainbow Dash tried to talk about the Wonderbolts, but Haystacks did not know much about them. He said what little he knew, and explained how he knew one of the advisors on their training from Cloudsdale U, but that was about it. They mostly talked about Cloudsdale and related matters the rest of the time.
After lunch, it was back to work. Now, Rainbow Dash got to practice cloud phasing directly. They switched back to using gathered clouds so as to not accidentally destroy part of Rainbow Dash's house. The first trial, she went through the cloud a bit too fast, overcompensating for getting stuck before, and dispersed the cloud. She managed to disperse it progressively less over the next few trials, but then got stuck again. This time she just broke the cloud to get free.
There were more trials. They even skipped the usual dinner time. It took the rest of the day, but Rainbow Dash managed to cloud phase properly a few time by the end of it.
"Hmmm... well done," Haystacks said, somewhat distractedly. He glanced over at the sinking sun and sighed. "Well, I guess that wraps it up for today. I've only got one more day here, and I've got to leave early the following morning, so tomorrow's all we've got."
"Yeah, and cool as this is, it doesn't seem like we're getting any closer to a Sonic Rainboom," Rainbow Dash said. Haystacks looked askance at her.
"I thought I explained... whatever, just wait until tomorrow. If I'm right, you should see a difference," he said, sounding a bit irritated. He tried to reign it in. He HAD explained it, but Rainbow Dash did not seem to be very good at retaining purely verbal instructions. Hopefully she would get the idea tomorrow.
"Alright, if you say so," Rainbow Dash said skeptically, "Same time tomorrow?"
"Same time," Haystacks said with a nod, "Rest up!"
"Oh, wait, I forgot," Rainbow Dash said, turning back towards Haystacks after she had started to head inside, "I have some weather stuff to do tomorrow. Been slackin', but I better get that done. Won't take someone as awesome as me but a few minutes. So just wait around... what, here or back at AJ's?"
"Oh, right, at the farm," Haystacks said, "I'll set things up while waiting. Just do what you gotta do." Haystacks gave an informal wing-salute then took flight back towards the center of town and his hotel.
Haystacks hoped something happened tomorrow, or he would feel silly about spending all this time on cloud phasing. A nagging part of his mind said that he had only gone down this route so he could show off, but when he examined the logic that led to this course of training, he repeatedly found it sound, so he ignored it. If nothing else, he had managed to teach a pony something new, which was something. In retrospect, it was downright amazing that Rainbow Dash had learned the technique in a single day. She truly was a rare talent. He would have to talk to his Wonderbolts contact about her.