Outside the gates of Tartarus, two of Cerberus' heads were resting, the other keeping watch through the dark and misty night. The heat and humidity would be near unbearable for mere mortal creatures, but to Cerberus the night was cosy and warm. The walls of Tartarus stood impossibly high, built with stones unfathomably thick and magically protected against even the most powerful of creatures.
However, in the darkness, amongst the shrubbery which surrounded the gates, lurked a stallion who had travelled far, far from home. An orange-coated pony with a pale nose and brilliant vermilion mane, wearing large, round spectacles over his eyes and a star spangled cape over his back. Sunburst had arrived at the gates of Tartarus with a plan: to tear down the wall and release what horrors it concealed upon Equestria!
With a simple whisk of his horn, a vast amount of powerful magic spread over Cerberus, like a giant blanket of twinkling stars over the beast. The conscious head noticed the magic immediately and barked to warn the other heads. All three heads of Cerberus barked and growled loudly at the cloud which slowly fell across him. As the twinkling lights descended, they pushed Cerberus to the floor, rendering him motionless on the ground.
Sunburst revealed himself from the bushes, staring longingly at the unguarded gates of Tartarus. His heart pounded and his breath quickened as he considered his next spell. He gave out half a smile in disbelief that he had come this far and was about to succeed in his plans, seemingly without a hitch. He briefly looked down to the ground, recalling the spell he had to cast. Finally, in firing up his horn and with a little stress and a lot of concentration, Sunburst fired off a powerful beam of electric blue magic which engulfed the gate and spread across the walls.
The metal bars contorted and the walls crumbled under the might of the magic on show. The heat of Tartarus spilled out around Sunburst as gigantic rocks fell by his sides. The gate eventually snapped, the doors flew from their hinges and fired themselves past Sunburst's shoulders, landing on the muddy grass behind him.
It took a moment, but quietly, a low rumbling emerged from the silence. The sound of stomping hooves, a marching army of darkness quickly approached the gates. Sunburst readied his penultimate spell - a spell which he hoped would bend the will of all the dark forces to match his own. He panted anxiously as a million stampeding atrocities stormed to the gate, and as they came into view he chanted a spell incoherent to anyone but himself. The banished and the burdened drew ever closer to their assumed freedom, aware that someone - or something - had destroyed the gate, but naïvely unaware of what dangers lay ahead.
As they escaped over the wall to freedom, those too stupid and unaware instantly found themselves under the cloak of Sunburst's spell. Vast armies of devilish minions suddenly found themselves succumbing to the might of his magic, whilst other, more intelligent beings kept their distance. Wave upon wave, abomination upon abomination spewed over the wall. Sunburst was barely able to maintain his excitement, letting out a mad, heckling cackle as his army grew in magnitude.
On the other side of the wall, from the darkest corner, a small, weak-looking Tirek looked on, muttering to himself, "The pony has harnessed magic far beyond his own capabilities. Far beyond the capabilities of his Princesses."
Sunburst's eye fell upon Tirek. He chortled at the feeble-looking centaur, "Come, Tirek. Join me!"
Tirek merely shook his head, "You know nothing of the powers you possess, pony."
Sunburst smirked, "And you do?"
"I have witnessed a power much like this in aeons passed. I cannot stop you in your plan, but surely you know you cannot hope to control the forces within you?"
"It wasn't my intention to control it. It was merely my intention to unleash it!"
Tirek gave no retort to Sunburst's strong statement, instead choosing to retreat back to the depths of Tartarus. He had no plans to escape his imprisonment.
As the final few creatures spilled out of Tartarus, Sunburst completed the final piece of his plan. His eyes turned a lime green, black smoke-like magic protruded from the sides of his eyes, and a team of black and purple orbs shot from his horn. The dark magic scarred the walls, leaving them permanently agape, giving any demon its chance of freedom.
Sunburst turned to his newly-formed army all glistening under the electric blue glow of his control spell. "This is it! Now is the time to reclaim Equestria! I have given you freedom. In exchange, you will give me the throne! Once Celestia and the Elements are banished to Tartarus for eternity, we will rule this world! Now go! Go forth and conquer everything!" Sunburst roared, and like puppets on his string, the amalgamation of millions of Tartarus' worst creatures ventured forth from the gatepost to begin their lengthy journey towards Equestria.
But as the crowds dispersed, the commotion settled and the last remaining sound was that of the burning fires of Tartarus, Sunburst was taken by surprise by a presence behind him. Tirek stared down Sunburst, gazing directly into his eyes. "Even with the might of all of Tartarus behind you, you shall not succeed, pony."
Sunburst stared back at Tirek, but with much less vigour, "What makes you so sure?"
Tirek grinned, "Equestria contains more power than you perceive. It will take much more than brute force to challenge them."
"So join me."
Tirek shook his head as he turned to walk away, "Silly pony. I am Tirek. I will never play companion to such an incompetent fool. No. The consequences of your actions are yours to bear alone. But have no doubts I shall be watching patiently for your inevitable fall."
Sunburst was somewhat shaken by Tirek's words, but refused to let it show, "I will take Equestria, and when I do, you'll be next, Tirek."
Tirek chuckled heartily as he retreated back through the fires. Sunburst shook his head and turned his back on Tartarus, opting to focus on more important matters: his domination of Equestria.