After picking up Applebloom at her dream fabric

Princess Luna headed off to collect the rest of the CMC, including its newest member Stone Mane in my Equestria dreamscape.
They stopped by Stone Mane’s dream fabric first for a couple of reasons. First. It was abundantly clear that Applebloom knew exactly how to find the colt’s dream fabric. Which further confirm Luna’s suspicions that filly had probably visited his when she was not around.

Second. While Stone Mane was nowhere as savvy as Applebloom when it came to navigating the Dream Realm. He still was more familiar with it than Sweetie Belle or Scootaloo were going to be, and Luna was going to want some ponies to her help navigate the other two to the destination across the shimmering veils of the realm.
Finding the other foals dream fabrics wasn’t a challenge although there were few delays in getting Sweetie Belle and Scootaloo focused on what they needed to do. Especially Sweetie Belle.
“Are you sure I don’t need to go before we leave?” Asked the filly. “Whenever I go on a trip with my parents or Rarity they always ask me before we leave. ‘Have you gone?’ Although if I am dreaming do I have to worry about going in my dreams? Oh! If I do go in my dreams will I accidentally wet my bed! I don’t want do that! I’m a big filly now!”
Luna shook her head but still smiled. “No dear Sweetie Belle. Unless your physical body needs to go you will be fine, and if do need to go you’ll just wake up as you normally would.”
So finally Luna was able to set off with her expedition team. At first it was slow going, but as Sweetie and Scoots got more familiar with the moving through the Dream Realm they picked up speed. The two fillies had only done this once before with Applebloom during the whole fiasco with the Mimic.

Finally Luna started leading everpony that evening’s destination.
For this reason Luna had Applebloom and Stone Mane positioned on the outside of her little formation. Applebloom on her right edge with Scootaloo, Stone Mane and Sweetie Belle on her left. Fortunately her Highness was familiar with the destination, and knew a route that was guaranteed to be free of encounters with the less savory residents of the Dream Realm. Which was good because she spent a good part of the journey answering constant stream of questions from the foals. Even Applebloom was curious about where they were going because she was being led into a part of the Dream Realm that she was unfamiliar with. All Luna would say was that they were heading for the Sea of Dreams.
“Trust me everypony. I think you’ll find tonight’s adventure to be most fun and exciting! Now, just so you know. We’re going to be leaving the Dream Shard that all ponies dream fabrics reside in, and heading to a completely different shard in the Dream Realm! This is a very rare experience that most ponies will never experience. This is going to be lots of fun but I do ask that you stay in close proximity to me at all times. Do you understand?”
Getting verbal confirmation from everypony Luna made slight course correction and started flying towards a strange, swirling matrix of ever changing patterns and glyphs. As they approached Luna’s horn flared and for a brief instant and the glyphs stopped. Flying forward the Defender of Dreams lead her party through a small opening in the pattern.
There was brilliant flash of light and suddenly the aurora-like veils of colors and the dark, space-like expanses had been replaced. Instead the ponies found themselves flying through a glorious cobalt blue sky dotted with white fluffy clouds. Several hundred feet below them was a tranquil brilliant turquoise blue sea that sparkled in the sunlight. Off in the distance the ponies could make out clusters of small islands and nearer to them numerous reefs. Applebloom called out.
“R’ we ah headed fer one of them islands yer Highness?”
The alicorn shook her head. “No. At least not at first. Everypony gather close to me!”
Luna’s wings suddenly stopped flapping although she remained aloft. The foals floated together until the they were under her wings. Satisfied with this the princess smiled at them. As she did her horn started glowing.
“Okay everypony listen to me. You’re going to be safe. Now.” Suddenly the mare pulled her wings in tight collecting the foals under them. Then everypony suddenly plummeted out of the sky toward the water below them. Falling headfirst toward the water Sweetie and Scoots screamed while Stone grinned and Applebloom whooped in excitement. As they approached the water Luna’s horn burst forth with a bluish white light that enveloping them all. They hit the water with a great splosh!
Sweetie Belle felt herself sinking deep into the warm tropical waters. She couldn’t see anything because of the enveloping glow and great curtain of bubbles, but she felt funny. Not right. Suddenly the glow faded and she found herself staring up at the surface of the water far above her. In terror she started trying to swim back to the surface, but her hind legs felt funny. Looking down she discovered they’d been transformed into a single, horizontal fin/tail that was striped in colors similar to her mane.
The filly was trying to wrap her mind around this development when Scootaloo came tearing by leaving a trail of bubbles in her wake as the filly’s new tail propelled her along. The orange torpedo was whooping up the whole time.
“Yeah! Awesome! Sweetie! Sweetie!” Scootaloo looped around and swam up to the still befuddled friend. “Sweetie Belle! Isn’t this so AWESOME!”
It was at this point that the unicorn/merpony realized that her friend was talking underwater….and she was breathing just fine. However Sweetie was still holding her breath. Reluctantly Sweetie exhaled and inhaled. She dreaded the idea of suddenly having her lungs full of water, but she felt nothing different from breathing on land.
Growing more comfortable with the situation, Sweetie tried to figure out how her tail worked. At first all she could do is send herself off in random directions and speeds, but with Scootaloo’s advice and practice Sweetie Belle started gaining control over her speed and direction. She had to agree with Scoots. This was fun!
Meanwhile Applebloom seemed to be perfectly happy with being a merpony and was enjoying this new form, for the most part she was keeping a close eye on Stone Mane as he twirled and floated around in the water.
For the next few minutes this random, free form exploration continued. However as the 4 foals gathered and were chatting a large shadow fell over them. Floating above them was Princess Luna herself a merpony now. Her silver and blue star speckled mane floated and swirled around her, and the sunlight from above threw sharp highlights on her glistening Prussian Blue body. With a smile on her face she addressed the foals.
“Now my little sea ponies. Let us see what the Sea of Dreams has in store for us tonight! And remember this is all a dream and no harm will come to you while you’re with me. Now! Let’s have an adventure!”
Then Princess Luna swam off with the fillies in tow.

To be Continued.