Meanwhile, at Hornguard.

After her meeting with Celestia, Luna went to Hornguard, where Arantir was waiting for her.

During the last night, the alicorn of the night moved the undead army she raised to the ancient city and hid it there. With the army hidden from anypony's view, Luna was finally able to relax.

Luna entered the throne room of the castle. Arantir was sitting on the throne, three books were slowly circling around him as he was reading them.

"Hello again, princess Luna." the necromancer greeted her.

"Hello, Arantir." she replied with a small nod.

"I called you here for the matters of most urgency and importance." he said, setting down the books. He stood up from the throne and walked down to Luna. "As you probably already know, there is a great danger. Most important is, that danger is not only threatening us, but our friend Andromalius. Maybe even the whole world."

"You figured out how to help Andromalius?" Luna asked.

"Yes, indeed." Arantir nodded. "Sombra believes that this barren land is his and his alone. We shall distract him by revealing this city. We shall melt the ice and snow, thus signaling him of our coming, making him notice us. He doesn't expect it. In fact, I certainly know that he is unaware of my and my army's presence here. He will be very, very surprised... And caught off guard. We shall be able to mess with whatever plans he has for Andromalius, thus giving our friend time to prepare a strike of his own. And then, Sombra will be defeated. I have faith in Andromalius, he is strong-willed."

"If it is so, we must act immediately." Luna nodded.

"Rightly said, Luna." Arantir replied. "We go now."

***

Arantir and Luna were standing on one of the towers in the center of the city. The undead army stood on the ground, patiently waiting for their commanders' orders.

"Now, follow my lead." Arantir's eyes started glowing green. "This is a powerful spell, and we need perfect concentration. Clear your mind and feel the energy rushing through you..."

Luna slowly inhaled, her horn started glowing.

"You feel the energy — it is warmth. It gathers together... And now, you unleash it, turning the ice and snow into water." Arantir said and opened his eyes; they were completely toxic green.

A sphere of mixed green and blue started glowing around the duo, and expanded, faster and faster. As it reached the ceiling of the cavern the city was in, the hard ice began to thaw, soon melting into water that started dropping upon the city like rain.

The sphere expanded further, turning more and more ice into water. Soon, a part of the sky was revealed. The water rushed down, streaming through the streets of the ancient city, and then went down the drains into the depths. Soon the whole city was free from the ice, standing proud among the cold lands. The pools of water that were left started to freeze.

"Well," Arantir spoke. "Sombra will notice us soon. We better prepare for the battle."

In the Darkest Realm.

"It seemeth thy friends are coming to save thee, Andromalius." Sombra spoke to the hell stallion. "How unfortunate that they shall be dead soon... I leave thee here to wait. As we all know, there is nothing more cruel than making someone wait when their friends are in danger. Oh, I shall bring them here for thee to see their last moments."

"They'll destroy you." Andromalius growled.

"Hm hm," Sombra chuckled darkly. "We'll see..."

The undead armies of both Luna and Arantir have taken the defenses Hornguard had. Fortunately, most towers and walls were still intact, and some even had working ballistas that haven't rotten through time.

"Feeling nervous?" Arantir asked Luna. She nodded in reply. "It is natural. But we have our armies. They are ready to die for the cause. And rest assured — they fight well, even in the state like this. Sometimes, they were better than the living."

"I hope you're right, Arantir." Luna sighed shakily. "I... I almost lost my sister to him. I mustn't fail now."

"And you shall not." Arantir assured her. "Remember what I taught you. You now know some battle magic that will come in handy soon."

The ground began to rumble, a big cloud of black smoke appeared on the horizon, covering the snow like a blanket. The sky began to turn orange, distant booming of thunder could be heard.

"He is here." Luna said, narrowing her eyes at Sombra's form.

"I am coming for you!" Sombra's snarl echoed through the snowy plains. "Your struggle is futile, ponies!"

"He doesn't yet know whom he's dealing with." Arantir said. "We have a few surprises up our sleeves... And I would have so much pleasure turning him into a dung-beetle once this ends."

"I cannot say I disagree." Luna replied.

"Oh, so..." Sombra spoke, coming rather close to the city, yet not enough for its defenders to reach him to attack. "You have a necromancer on your side? Oh how the mighty have fallen! Calling to the powers of dark to defeat me? Where is your power of love and friendship now? You have an army? I have my own, too..."

A large army of crystal creatures appeared from behind the dark smoke, and started marching towards the city. There were many dark crystal ponies, distorted figures, and a few black crystal dragons.

"You cannot win!" Sombra taunted. "My army shall shatter your puny bones into ashes that shall be buried after your inevitable defeat!"

"Luna, take the second exit of the city." Arantir told. "He might try to attack from there, and we must be ready for this. Relocate your army, I shall remain here."

"I'm on it." Luna nodded, and took off into the sky.

Using her magic, she telepathically ordered her troops to relocate. Her army started marching through the city.

Soon, Luna landed on a big tower that stood in front of the second gates. She could already see the dark army trying to get closer. However, her own troops were ready to fight, standing behind the gates, on walls and towers.

"Well, here it goes..." Luna muttered, remembering her leadership skills. She knew her present army is the most obedient, and yet she was not sure how to command it. So, she sticked with the way she used to. Though, nothing was spoken but telepathically ordered.

The troops arranged in different formations, preparing to defend the city at all cost, even their... un-lives.

Andromalius and Will were walking through endless crystal halls. Something changed, though, and they've noticed it.

"I feel... something." Will looked around. "Like something around us... changed."

"Sombra left to fight." Andromalius replied. "Perhaps something changed with his departure... It's like some pressure was lifted off of us. Perhaps, his presence makes this world even darker. Without him, some things just don't work like he wants them to."

"He hath never left before." the crystal pony shook his head. "Did he even have to? It's his world... Inside his head. Nopony can leave their heads, right?"

"There's something we don't know, then. We need to investigate... Who knows what we'll find." Andromalius replied. "Maybe he's just fooling us... You never know."

As Sombra's army was coming closer and closer to the city, the defenses began to do the work. Ballistas started shooting at the coming army, sometimes shattering small crystal figured but mostly missing. Luna and Arantir were throwing spells at them, but most were deflected completely due to the magic-reflecting nature of crystals.
The crystal dragons were high up in the sky, searching for something to destroy with their dark fire. They couldn't be reached by ballistas nor magic could harm them. They were the rulers of the sky with no one to bring them down.

"You have no dragons at your side!" Sombra laughed, taunting his enemies.

Suddenly, the sky above Hornguard began to turn into something different... As if a giant knife cut the space itself. Soon, there was a great big hole, showing night skies and two moons. A roar came from the hole, and a black dragon flew in. It wasn't a regular dragon — it was Spectral Dragon, a bone dragon. Not only all its bones are from different dragons, they were and influenced by powerful dark magic, making them completely black. Using its skeletal wings, it descended and landed on the highest tower. The green eyes of the creature scanned the surroundings.

The Avatar of Death was summoned.

The dragon roared again and took off to the skies, beginning his hunt on the crystal dragons. Its green eyes glared at the prey.

One of the crystal dragon tried to attack the Avatar, but the hit was evaded. As that crystal dragon flew close to the Avatar, the latter bit into the side, and ripped a large chunk of crystals. Quickly, the Avatar bit into one of the crystal wings, shattering it with strong and sharp teeth. The crystal dragon cried in agony, falling to its death.

"'Tis but one dragon, and I have an army of them!" Sombra snarled. "My army is infinite! You and your undead dragon shall fall before me like many others have!"

Andromalius and Will still walked through the halls, trying to find anything that can help them defeat Sombra. Soon, they came to a large door made of dark wood.

"I know this door." Will frowned. "I don't want to touch it."

"Why?" Andromalius asked.

"If I do that, the sensation that cometh next won't be pleasant." he shuddered. "It's like... Everything inside starteth to melt and... It's like I'm pulled in all directions at once." he took a step back. "Never do I touch this forsaken door again."

"Maybe Sombra has something there that will help me defeat him." Andromalius tapped his chin. "Will, wait here, I'll try to enter."

The hell stallion warily approached the door. Hesitating a little, he pushed the door. To his surprise, nothing happened to him and the door opened. However, he couldn't see what's inside.

"If I don't return and Sombra does," Andromalius turned to Will. "Consider me dead and try to fight on your own."

"I'll... Alright, I..." Will stuttered. "But I shall be completely alone... I don't want to. Thou art the only one alive I've seen here in many years."

"Sometimes, it takes a sacrifice to win." the hell stallion replied. "It may be inevitable... However, everything must be done to evade it. This is how victories are made."

"Maybe thou'rt right. And I haven't seen anypony like thou before." Will replied. "Even if thou lookest... strange, it dothn't mean thou art a bad pony. Thou art the only exception I've seen to the universal rule — bad looks equals bad attitude."

"Judging a person by the looks isn't reasonable." Andromalius shook his head slightly. "The reason such people act bad may be based on how they were treated. It doesn't matter whom you're treating bad — you shouldn't expect them to be kind to you once they grow up enough to fight for themselves.

"There is a simple chain of logic. Action — reaction. It's a rule to treat others the way you want to be treated, and visa-versa."

"Uh, I think thou'rt right." Will scratched the back of his neck. "Though... Maybe not entirely. So... Good luck, thou needest it there."

Andromalius stepped through the doorway. It was even darker than in other halls. As he entered, the door closed behind him.

He felt that the place was putting much pressure on him. It wasn't silent — something like whispers could be heard. There were also silhouettes in the corner of his eyes, and yet he couldn't see them clearly.

Andromalius knew that whatever lies ahead is way dangerous than anything else he's encountered before.