Although Sombra implied that he would teach Twilight a new spell after only one day, it was several before he was satisfied with her control of Dark Magic. Ironically, Twilight's frustration at the delay only aided her. However, one morning, things changed.
'You will not be practicing control today.' Sombra said telepathically, as Twilight came downstairs one morning, to see his crystalline form resting on her new desk. 'Something is coming, and I sense that you will need to be at full power to face this challenge.'
'What do you mean, you "sense" it?' Twilight thought back, having gotten the knack for such communication over the time since Sombra had cast the spell for it.
'When you have mastered both Unicorn and Dark Magic, you begin being able to sense powerful sources of magic before they reach you,' Sombra explained, having come to truly enjoy his role as teacher, with such a gifted and attentive student. 'That is how I knew that the Two Sisters were coming for me a millennium ago, and had time to cast my curse over the Crystal Empire.'
Twilight frowned at the reminder of her new teacher's past crimes but shrugged it off. He was harmless now, and once she learned his magic, she knew she would be able to put it to good use. 'So, what's this "challenge" going to be? Are you sure it's not just one of the Princesses coming for a surprise visit?'
'It is not.' Sombra replied with undeniable certainty. 'What I sense is Dark Magic, and I am unaware of any practitioners beyond us two, so I cannot say what form it will take. Since we cannot prepare without making assumptions that could lead to mistakes, I would suggest resting, and being ready to react to whatever may come…'
Twilight nodded at those words. With a flick of her horn, Twilight levitated the crystal off her desk, and slipping the string over her head, before letting it fall to hang around her neck like a pendant. When Spike had noticed it, Twilight had simply said that it was a good luck charm that she had picked up when Cadance had asked her to come back to the Crystal Empire. Fortunately, the baby dragon had believed that, keeping her from having to come up with anything else.
As if summoned by her thoughts, Spike came downstairs at that moment. Yawning, he said, "Are you heading out already, Twilight? You should have woken me up! Besides, I'm sure Fluttershy won't mind if we're just a couple minutes late."
"What are you-?" Twilight started, before remembering what she had planned, before finding Sombra and beginning her studies of Dark Magic. "The show for the representatives from Saddle Arabia! I had completely forgotten!" Levitating Spike onto her back, Twilight rushed out the door, and began her way towards Fluttershy's home at a full gallop.
'Care to explain, my dear student?' Sombra queried, curious as to what had thrown her into such a panic.
'Princess Celestia will be welcoming some foreign dignitaries from Saddle Arabia in a few days, and she asked me to put on a magic performance as entertainment.' Twilight answered. 'However, I got so caught up with the idea of learning Dark Magic that I completely forgot to practice!'
Sombra chuckled and commented, 'I'm not sure whether to take pride in having such an attentive student, or scold you for forgetting a royal directive.'
Hearing that surprised Twilight, prompting her to ask, 'I thought you hated Celestia for sealing you away. Why would you care what she wanted me to do?'
'Oh, I despise her most heatedly for robbing me of so many years.' Sombra replied venomously. However, he went on in a more respectful tone, 'That said, I cannot deny the accomplishment of maintaining a kingdom and staying in power as long as she has. Consider it respect for a worthy opponent.'
'I suppose that makes sense.' Twilight thought back. Seeing Fluttershy's hut come into sight, she mumbled, "Hopefully today's practice will let me make up for lost time."
Fortunately, her practice went smoothly. In fact, Twilight noticed that after all her practice to control the volatile Dark Magic, normal Unicorn Magic was a piece of cake to perform, even the complex levitation patterns she was doing with Fluttershy's animals.
However, as her practice came to a close, a familiar rainbow blur flew towards them at high speed. Crashing into Twilight in her rush, Rainbow Dash cried out, "Twilight! Come quick! It's an emergency!"
Twilight, Spike, and Fluttershy quickly followed the pegasus back into Ponyville. On the way, Sombra's voice sounded in Twilight's head once more, 'I look forward to seeing how you deal with this, Twilight. Consider this your first test.'
Sombra's words left no doubt in Twilight's mind that this was what he had had sensed earlier. When the group entered Ponyville, they found a commotion in the center of town. And at the center of the commotion was a familiar light blue unicorn.
"What's going on here?" Twilight demanded.
"Well, well, well," the unicorn said, as she noticed Twilight's approach, "If it isn't Twilight Sparkle."
"Trixie," Twilight growled, glaring at her, as she remembered the trouble she had caused last time she was in Ponyville.
"What's she doing here?" Spike grumbled, clearly no happier than Twilight to see the troublemaker.
Twilight missed what was said next, as Sombra's voice echoed in her mind. 'Th-That can't be! I never finished it, so how is she wearing that!?'
Twilight was surprised. This was the first time she had heard genuine shock in the shadowy king's voice. Looking at Trixie, she noticed the other unicorn was wearing something strange around her neck. 'What is that?' Twilight thought back. 'I know I've seen that amulet somewhere before…'
'That is the Alicorn Amulet.' Sombra replied. 'I designed it to amplify the powers of any user who wore it, as well as amplifying their emotions to aid in wielding Dark Magic. But, I don't understand! I was sealed away before I could finish it, so how is it before us now?'
'The Alicorn Amulet?' Twilight repeated before her eyes widened in recognition. 'I've read about that! According to my books, it grants incredible power but corrupts the user. It was made by Starswirl the Bearded almost a thousand years ago.'
'I see,' Sombra thought back, understanding making his tone calm once more. 'For all their claims to eschew Dark Magic, it would seem that the Two Sisters had no qualms about passing on my work to their court wizard.'
Before the communication could go any further, Twilight was pulled back to the present by the sound of Spike crying out. Seeing Spike curled up in a ball, and being bounced by Trixie's Magic, and her other friends effected by various enchantments as well, Twilight gasped.
"Do I have your attention now, Twilight Sparkle?" Trixie said, with a smirk.
"Stop picking on my friends, Trixie!" Twilight demanded, glaring at her once more.
"You and I have some unfinished business," Trixie said, her tone overflowing with confidence. "My magic's gotten better since I was here last, and I'm going to prove it! Me and you; a Magic Duel. Winner stays, loser leaves Ponyville… forever!"
Twilight was about to call out Trixie for obviously trying to use the Alicorn Amulet to win such a competition when Sombra stopped her. 'Accept her challenge, and let her use that Amulet.'
'What? Why should I let her cheat!?' Twilight protested telepathically.
'For one, if that Bearded fool made my Amulet right, then the wearer is the only one who can remove it, anyway.' Sombra explained. 'In addition, I told you this would be your first test. You cannot expect your opponents to always fight fair, so you must learn to find ways to overcome foes that are more powerful than you. First, you will attempt to do so on your own, and I will observe. Then, if I feel it is necessary, I shall step in to correct your method.'
Twilight frowned. Sombra's method of teaching was as different from Celestia's methods as shadow was from light. When it came to magic, Celestia had encouraged book learning and explained things carefully to make sure Twilight understood what she was doing before attempting anything while Sombra seemed to be a firm believer in learning from mistakes, letting Twilight do things the wrong way, and then correcting her.
However, Twilight had more important things to worry about at that moment. Focusing on the expectant Trixie once more, Twilight said, "Alright, Trixie, let's duel!"
"Excellent!" Trixie said with a grin, undoing the magic she had cast on Twilight's friends. "If I lose, I won't set hoof in Ponyville again," Trixie went on, "but if you lose, you're the one banished from this one-horse town!"
With that said, the two unicorns stared each other down, the tension mounting for a moment, before Trixie shouted, "Draw!" She fired off a quick beam of magic at a nearby cart, launching it into the air, and causing it to fall towards a group of onlookers. However, a quick telekinesis spell from Twilight let her levitate the cart and its contents safely aside and putting her on equal footing with the other unicorn.
Trixie did not let up her assault, launching spell after spell. However, Twilight countered each and every one, although it took nearly every magical trick she learned. The duel seemed tied, neither being able to outshine the other, until Trixie used her ill-gotten power to perform a particularly powerful spell.
"Snips, Snails, step forward." Trixie suddenly said, summoning two unicorns that were her die hard fans.
"W-What is it, Oh Great and Powerful Trixie?" Snips said as he and Snails bowed before their idol.
Trixie did not bother to explain, merely blasting the pair with her magic. When the light cleared, Snips had been reduced to a foal, and Snails had been aged to be an elderly stallion.
"An Age Spell!?" Twilight said in shock. Such a spell would have been impossible for all but the strongest of unicorns, but knowing about the Amulet that Trixie was wearing explained that. Twilight doubted that she could perform such a spell herself, but knowing that Sombra was using this situation as a test, Twilight was determined to impress. Focusing her magic, Twilight let it wash over the transformed pair, trying to shape it as she wanted.
However, she just could not muster enough magical power. Her spell fizzled and dispersed, and in the end, all she did was wear herself out.
"I am victorious!" Trixie let out a maniacal laugh, before declaring, "And now, it's time for you to leave Ponyville… forever!"
"That's enough, Trixie!" Applejack shouted, as she and Twilight's other friends jumped in front of her, in an effort to dissuade Trixie from enforcing that banishment.
Although Applejack wasn't the only one to protest, Trixie cut them off. "You fools!" She cried, as her magic gripped Twilight's body. "She's already gone!" Suiting words to action, Trixie used her magic to send Twilight rocketing backward, all the way out of town.
As Twilight felt the magic release her form and got back to her hooves, it was only to see Trixie lowering a magical barrier around Ponyville, trapping her outside, and the other inhabitants within.
'Disappointing, but not unexpected.' Sombra's voice appeared in her mind.
'And where the hoof have you been!?' Twilight thought angrily, as she glared down at the crystal hanging around her neck.
Sombra was unperturbed by her tone, however, actually encouraging it, instead. 'Harness that anger, my dear student. You will need it for what comes next.'
'What do you mean?' Twilight thought back.
'Why, getting back into your home, and making that fool pay, of course.' Came Sombra's response. 'You will need to harness Dark Magic to cast the spells I shall teach you to accomplish that, after all.'