Starswirl and Somnambula heard hoofsteps below them and saw a hooded figure with a red horn holding a gold scepter with a ruby on the end step forward. Starswirl leapt down onto Sombra with a shout, "Now!"
Starswirl tackled the stallion to the ground, knocking the scepter away. Once he stood back up, however, he noticed the horn and hood had fallen off, revealing the forepony.
"Well, well, well," said a deep voice from behind Starswirl. As he turned to face the voice a blast of magic encased him in a translucent crystal. "What have we here? Another unicorn come to challenge me?" The speaker stepped into view. He was a tall dark-grey stallion with an ethereal black mane, a red cape with white trim, a silver collar and matching crown. What really stood out though, was his horn. It was red, as Starswirl knew it would be, but it was also curved, unlike any other unicorn Starswirl had ever seen. This, then, was the true Dark Wizard.
"You thought to steal this," he said, holding a light grey crystal staff with a large ruby on the end. "But I have managed to outwit your clever little scheme. What do you have to say now! Hahahahaha!"
Somnambula swooped in, stole the scepter, and began flying upwards. "What? Get back here with that!" Sombra yelled as he fired a magic beam at her. It hit her left wing and sent her spinning down into the courtyard. "You, go get my staff back!" He pointed at the forepony, who immediately galloped off. Sombra looked back to Starswirl just as he managed to destroy the crystal prison. "Alright now to deal with you."
Starswirl fired a magic beam of his own at Sombra, only for Sombra to make a black crystal grow up from the floor, blocking the shot. "It's cute you think that will do anything," quipped Sombra as he caused several more crystals to grow in a wave. Starswirl teleported past Sombra and his crystals just before the last one burst though the spot where he was standing.
Starswirl fired a magic beam at Sombra from behind. "I don't know what you are," he said as Sombra whipped around to face him and met his beam with another one, "but I've been practicing magic my whole life, why don't you just stand down."
"How about... No!" Sombra shouted as he overpowered Starswirl's beam. Starswirl jumped to the side as the black and blue torrent of bubbling energy tore a chunk out of the stone floor.
"How did you know to set up a decoy?" asked Starswirl. He glanced into the courtyard looking for Somnambula but quickly scrambled around the left corner to avoid Sombra's beam that came when his attention was divided. Sombra walked forward until he was standing on the inner wall just twenty feet from Starswirl.
"I saw you and your pegasus in town and figured you would try to stop me from killing anypony. Your bleeding heart is going to be the end of you. Along with my magic, of course." And with that Sombra fired another magic beam, but Starswirl was expecting it. He had cast an illusion of himself and turned himself invisible. While Sombra had been talking he had silently teleported over to the right side. When Sombra fired his beam, so did Starswirl. Unfortunately it bounced off of Sombra's silver collar.
"Well, that was a clever trick, but you cannot hope to defeat me! I am Lord Sombra! Try as you might nopony can rival my magic!" Sombra fired a beam of magic at Starswirl, who responded by raising a shield spell. "You can't keep this up forever!"
Somnambula cried out as Sombra's magic hit her wing, causing it to break. She lost control and crashed into the courtyard. Fortunately most of the taken were outside but two were guarding the main entrance, and they immediately began galloping toward her.
"Halt!" they droned in unison. She decided not to comply.
Picking up the scepter in her mouth she mumbled as she ran, "You are free. If you can hear me please come help us. We are at the keep." She burst through the right doors, finding a hallway stretching both directions and a table on either side. She shut the doors and dragged a table in front of them just as the taken slammed into the doors.
After taking a moment to catch her breath Somnambula heard somepony coming from the right. She turned and saw the forepony galloping after her. She set off to the left and ducked into the first door she came across.
"You are a strong wizard to withstand my power for so long," said Sombra. "But I can tell you are weakening. Since you have proven yourself capable I will let you live."
"And why," asked Starswirl, "would you do that?"
"So that you will serve me, of course."
"I would rather die than serve the likes of you!"
"Well, unfortunately for you, I won't be offering you that choice." Starswirl's shield cracked under the pressure of Sombra's attack. "And now we begin." With a final push Sombra destroyed the shield. Then he formed a cage of black and blue crystals around Starswirl. Sombra's eyes began to glow green. The green seemed to expand from his eyes outward until it was all Starswirl could see. Then everything went black.
Starswirl looked around and saw his castle, the one back home in Rex Civitatis, burning down around him. He tried to send a signal flare up, but his horn would not light. He tried to conjure water but again nothing happened. He called out, "Guards! Friends! Anypony! Help!" All the time trying in vain to work any magic and stumbling down the hallway, looking for the exit.
As Starswirl stopped struggling and sagged in defeat Sombra's eyes faded back to red and white. "Much better. Such a waste, using your magic to help others. But now you can do that for the rest of your life. As for me, I would much rather be served than serve others." A rhythmic flapping sound began to grow audible. "Ah, like this one here," said Sombra, pointing at the dragon approaching the keep. "And now, with your magic and his strength to aid me, perhaps I will set my sights on bigger prey. You must have come from somewhere, I can invade that. And nopony, nay, nocreature, can stand in my way!"
While Sombra spoke Antiquorum had reached the side of the keep and landed. As Sombra began to laugh the great dragon bent down and swallowed the dark mage whole, incinerating him to ensure there would be no survival.
With Sombra gone everypony stopped and looked at Antiquorum. The taken all blinked and shook their heads, then everypony began to rejoice. Starswirl blasted apart the crystal cage and called out, "Thank you for your timely assistance."
After the banging on the other side of the door stopped Somnambula heard the forepony say, "I think you can come out now. My head is mine once again."
She removed the bunk she had placed against the door and cracked it open. "I think we should go see what has happened."
"Agreed."