*ring ring ring* Three o'clock. In the morning. Sky looked out the window of her cloud home to see nothing but pitch black with a silver crescent in the sky. The moon was waning, and it was almost gone. Sky had seen this before. She knew it was just another night, with the same old dream, but she couldn't help feeling scared. She was waiting for her sister, just like every night prior, only for her not to return. Over two and a half thousand times, seven straight years, she had this dream. She saw the same shadow at the end: A dark unicorn figure with a crooked curved horn.
Sky knew this to be the shadow of Sombra, former king of the Crystal Empire, who was overthrown by Midnight Twinkle and her friends with the power of love. Why was he in her nightmares, though? She was just a filly, and she had never even set hoof in the Crystal Empire, much less on the day of that battle. Why was he, king of shadows and destruction, living inside the mind of this one filly, who hasn't left home since her mother passed away? The only pony Sky could ask about Sombra was her sister, Midnight Blue, but she hasn't been seen since the Crystal Empire was saved for the third time... the day the Changelings were reformed.
Sky knew the only solution was to go to the Crystal Empire and ask her sister about the Changeling invasions and King Sombra, and possible connections between them, but she didn't know how to travel there. The train was obviously not an option, as that was run by Cadence and Shining Armour's Royal Guard, who would recognise a former Rainbow Factory worker's sister and send her straight back home. Flying, she would be too clearly visible by day and too tired by night to make any headway. Walking, the Summer Solstice would arrive too soon before she got there, and she'd be just a face in the crowd for next year's Summer Sun Celebration. She could teleport, but she needed to find a skilled unicorn mage willing to go with her.
So it was that Sky Blue thought to ask her friend Sweetie Belle for help. After all, she'd been learning magic from the Princess of Friendship herself for over a year and a half now, she must've mastered teleportation! Sky snuck down through the skies, and then landed in Ponyville, where her friends, the Cutie Mark Crusaders, lived. All she had to do now was find their clubhouse, and she already knew where it was: on a secluded part of Sweet Apple Acres. Sweetie Belle usually practiced singing at three-thirty in the morning anyway, so now would be a good time to ask her. The two of them could sing along the way... in case the teleportation didn't work. If it did, they could sing when they got there. All Sky had to do now was call out for her friend.
"Sweetie Belle! It's me, Sky Blue!" Sky hollered into the clubhouse. Maybe she's not here yet? Sky thought. It is about twenty minutes early... maybe I should just wait inside the clubhouse? And so she waited. And waited. Eventually, even in the pitch dark, Sky could make out Sweetie's face.
"Sky Blue!" Sky heard Sweetie calling. "Over here!" Sky saw Sweetie in a tree, next to the clubhouse rather than in it. "Quickly!" Sky flew up to the tree branch.
"What are you doing?" Asked Sky.
"Hiding from that!" Sweetie answered. She pointed a hoof. "Don't make another sound." Sky looked down to see a pile of branches in the shape of a wolf. She knew it was a Timberwolf, but she thought they were only twice as big as ponies. This one was about seven times as big as an average size Timberwolf. "That's Arboralupus Rex, king of the Timberwolves. He stole something from Rarity and I'm going to get it back."
"Are you out of your mind?!" Sky asked, not realising how loud she was being. "I thought you said not to make another sound! The king could probably smell us anyway though..."
"I guess I hadn't thought of that." Sweetie replied. "How am I gonna get that Fire Ruby back now?"
"Wait... you lost Rarity's Fire Ruby!?" Sky asked. "And it was stolen by the Timberwolf king? Not the Dragonlord?"
"Ember wouldn't steal a gem from Spike's friend, Sky." Sweetie replied. "Rex on the other hoof... er... claw... was brainwashed by King Sombra's son, but even if he wasn't, he'd take the Fire Ruby and combine it with the Ice Sapphire and the Nether Emerald to make the Star of Illusions. I read about it in one of Twilight's books. These three gems hold mystical powers, and when combined, they make a gem that could destroy the universe... and replace it with a new universe of pure evil!"
"That sounds a lot like the Chaos Heart." Sky responded. "The bringer of destruction mentioned in the Light and Dark Prognostici. Lord Blumiere, who changed his name to Count Bleck, created it with Princess Celestia and Discord's sham wedding, then an evil mage named Dimentio stole it when Blumiere was an inch from death. Dimentio then combined his power with that of the Chaos Heart and that of a green stallion named Lucian to make himself a super demon. He wanted to create a new universe which he could rule as king, but he was defeated in the end by Lucian's sister Aurora, as well as Princess Celestia and Discord."
"Wait... Discord helped Celestia defeat an evil mage BEFORE he was reformed?" Asked Sweetie Belle in confusion. "Let me guess... his rise to power was after their friendship ended, wasn't it?"
"I guess so." Sky replied. "I wonder if one of us will become evil at some point. I can only hope that we don't, but... who knows? Anyway, if the three gems combined could create an evil super gem, I guess we just have to destroy one of them... preferably not the Fire Ruby, as that was a gift to Rarity."
"We'd better get moving, then." Sweetie Belle responded. "The Ice Sapphire is in the Crystal Empire, and the Nether Emerald is in Tartarus. We can't linger here much longer, and we could take care of the Timberwolf king after destroying one of the other two gems. Let's go to..."
Sky exclaimed "The Crystal Empire!" at the same time that Sweetie exclaimed "Tartarus!" Sky looked at Sweetie in confusion.
"Teleportation can instantly take us to the Crystal Empire, but there are too many ponies there." Sweetie explained. "The guards of Tartarus only focus on the prisoners, so it'd be much easier to sneak around there." Sky could only hope that Sweetie was right... they had to literally go to Tartarus and back again.