Marshal Malice's descent into Tartarus wasn't pleasant. Or easy.
He first had to travel to the Cursed Mountain, so many leagues away, in the darkest, most recluse corner of the known world. He had to then walk up the mountain, to the gates themselves, sneak past Cerberus, and walk through the dank, musty tunnel to reach the vast space inside.
The tunnel he had walked through had taken him to another dimension- the dimension of Tartarus, contained inside the Cursed Mountain. Great mountaintops stuck up all over the place like corroded teeth. In those mountains, encased inside, were the most hardened, vile, and cruel beasts imaginable. In the valleys between them ran rivers of black burning pitch alongside high banks of sharp obsidian shards.
He eventually came to the Cave of Tongues, a place where divine messages could be given to any who entered... worthily. In one of the farthest corners of the entire dimension, the journey to reach it had taken him more than a day, even with the rare gift of teleportation. Tartarus exuded a foul force that blocked all outside magic, except for the creatures gifted by the king of Tartarus himself.
Malice entered the cave with trepidation. Malice was afraid. It didn't happen often, but there was only one creature alive that Marshal Malice truly feared. And that was his master. The king of Tartarus.
The cave was a tall, cavernous space made out of dull black rock. It was about thirty feet in diameter and at least fifty feet high. Malice looked around nervously. His master would not be pleased.
A deep rumbling and cracking came all around him, emanating from every corner of the room. Malice flinched. The confined space seemed to shrink around him. It then subdued into a deep, steady rumble. The room seemed to be waiting for him to speak.
"M-master," Malice stammered, aware of his master's wrath, "I have...bad news."
The rumbling got deeper, more sinister.
"The Equestrian princess...we- I was unable to deliver her to you." Malice closed his eyes, certain his time had come.
Why? the most terrible voice ever created cracked around him. It seemed to permeate every part of Malice. It came from the rock itself. The voice, the terrible, terrible voice...
"B-because I had failed, Master." Malice trembled. He bowed himself down. "I was unable to stand against her and her protectors." He braced himself, certain that his time had come at last to die in Tartarus.
What protectors? the awful, deep voice demanded of him.
Malice opened one of his four eyes, somewhat surprised his master hadn't blasted him into oblivion on the spot. He gulped and said, "The Guardians of the Sun, Master. They rescued her from her clutches."
The cave made a humming sound, as if contemplating Malice's answer. Malice would flinch involuntarily every time it raised in volume, even for just an instant. A few pebbles dislodged themselves from the walls and lay in the dust covering the bottom of the cave.
I have heard of those three, the voice rumbled in disapproval. Those have been a continual thorn in your side for a time now. Why have you not plucked it out?
Malice went stiff. "Because they-"
Because they were more powerful than you, his master snarled, and a few more pebbles rained down. Malice felt a rush of fear for his very soul. Three underlings of Princess Celestia were more powerful than Marshal Malice, the slayer of the Rada, the untold terror of the unknown world, the leader of the armies of Tartarus. I am disappointed, Malice. I have every right and privilege to have you thrown into the Pit of Despair for your inadequacy.
Malice prostrated himself on the ground in shame. "Do it, then," he whimpered. "I deserve it. I am a worthless servant."
An evil, evil laugh echoed around the chamber, piercing Malice's soul, making him put four of his arms over his pale head and cower like a fool. The awful, nightmare voice then stopped the laughter, making Malice freeze in anticipation.
Get off the ground, my servant, his master commanded him.
Malice jumped off the ground and stood up straight.
Have no fear, Malice. You will not die this day. I am a merciful god. You are far too valuable to replace easily.
Malice let out an exhale he didn't know he had been holding in.
But know this, the terrible voice of the king of Tartarus said, and Marshal Malice's head snapped up. Your work is not finished. I swore to Faust that I would be free once again. I need an Equestrian princess. I command you to lead an Equestrian princess- I care not which- to the Corrupted Element. Only then can I be free to rule the universes as I once did before. The time is drawing closer and closer when we shall unleash Tartarus's wrath upon the lands above.
"B-but what about the Guardians of the Sun?" Malice asked fearfully. "And the Elements of Harmony?"
Another laugh echoed all around the cavern. All in good time. Do you have any Fallens from Mount Nevermore?
"Y-yes, Master. Cookie Cutter has one available. Mount Nevermore's population is growing rapidly."
Can you think of a place to send him?
"The Everfree forest comes to mind, Master."
Station him there. We must have all of our pieces in place before we can play our game. We will not act until the iron is hot. But soon the time must come when the sun will not give forth her light, when the moon shall become red like unto blood, when the stars shall fall from their firmament, when the heavens shall tremble and quake, and the earth under their hooves shall be rolled together like a scroll. And from the ashes of this world shall rise a new order. An order of... peace.
Malice bowed himself once again. "Your wisdom is never-ending, my Master."
Unbeknownst to either of them, a creature had been listening at the mouth of the cave, listening in on every word spoken in there. The creature hurriedly pressed himself against the sides of the rock in terror. He tried to get his breathing under control.
Finally he whispered, "I have to warn Celestia!"