What is This Alternate World?

Day dawned in Equestria, the birds were singing, Celestia's sun was shining, the clouds were white but the sun nearly finished rising. The birds made such a nice song with their tweets, it was like a wonderful symphony was playing in their town, the towns and cities that made up Equestria.

The mane six had a couple days of residence in the Crystal Castle that was located at the Crystal Empire; you won't believe who came too, the Cutie Mark Crusaders!  They only did want to come because everything gleamed so bright, and to get their Cutie Marks.  Each of the guest rooms were humongous!  Everypony seemed to be asleep though, that's why you could only hear and see birds out there.

Sweetie Belle burst out of bed; that burst made her duvet spring into the air and on to the ground in front of her bed.  She opened her window and shouted, "Good morning, Crystal Empire!  Hope you all have a gleaming day!"  Sweetie chortled at her corny joke, making everypony wake up.

As Scootaloo woke up, she slammed her head against her pillow.  "Sweetie Belle, do you have to shout out the window?" she said miserably peering at her.

Sweetie smiled, "Of course I do!  What else makes you sleepyheads wake up?"

A light snore was heard from the edge of the room, which was Applebloom's side.  Scootaloo opened a enormous drawer, it showed a crystal flugelhorn.  She trotted over to Applebloom and played the flugelhorn, the tune streaming into Applebloom's ears.  Applebloom tossed the pillows onto the floor, then getting up on the opposing side.

Scootaloo held down a pillow, trying to rip it.  Applebloom trotted over, giggling.

"Need any help?"

Scootaloo groaned and then replied, "Please.  I bet you can't rip this."

Applebloom shrugged, "Why are ya tryin' ta rip tha pillows anyway?"

Scootaloo groaned, "I'm testing my strength everyday!  Only to be like Rainbow Dash."

Applebloom nudged her to get her attention, "How about we go eat breakfast, then ya test yer strength?"

Scootaloo sighed, "Fine."  The trio trotted into the kitchen, taking seats next to each other.  The mane six walked in, having a random conversation.  They sat down also, smiling at the CMC.

"Howdy girls, how'd y'all sleep?" Applejack asked.

The trio said in unison, "Good!"

Rarity levitated cereal, placing some into the Cutie Mark Crusader's bowls.  The unicorn then put the cereal box down.  A light cornflower blue aura surrounded the milk, Rarity reenacted the same thing.  The crusaders ate their breakfast, then peering at the six.

"Done!" the three then trotted away.

Scootaloo spotted a hidden room, so she lead them to there.  A mirror was shown, not just any mirror they thought it was, a mirror to an alternate universe.

"What's this?" Applebloom glanced at it, then her direction of her head went to Scootaloo.

The Pegasus shrugged, "I don't know this - but I think it's a portal to an adventure."

Sweetie looked at it, "Shiny!"

Applebloom sighed, "Y'all think it's a good idea to enter?"

Scootaloo gasped, "Are you seriously going to ask that?!  Let's go right now!"

Scootaloo hopped in, Applebloom and Sweetie Belle followed along.  Their vision faded away once they entered the portal...