It took the Scourge some time to finish off the rest of the living in the timeline Sunset was staying in, though the amount of raised dragons certainly aided them in that regard, especially with at least four of each Aspect, save Deathwing, aiding them in their efforts. The blue flight continued to move the undead across the lands, allowing them to ravage the living without allowing them to escape, while the red and green flights spread death from above, leaving all of the bronze and infinite dragons to ready themselves for what Sunset had in mind. She was intending on wiping out everything on this world, as in end all life, before worrying about her own timeline, but what the two time flights were focusing on was merging a piece of this timeline with the one she came from, allowing her to transfer all of the Scourge to her Icecrown and surprise the army that Tirion must have built. Basically put it was a massive teleportation spell across timelines, hence why the time dragons were focused on it while the other dragons were slaughtering everything else in the world, all while she readied herself for the final stage of her current plan.
Eventually, without any need for her to do anything, the Scourge wiped out all life in the timeline she had created, giving her a massive army that gathered in the icy region of Icecrown without bothering to rest at all, with the blue dragons making all sorts of platforms so everyone could stand in this region.
"The army has gathered, as per your orders." Chromie said, where she and the other members of the Council knelt behind Sunset as she stared out at the army of undead and dragons that was her version of the Scourge, in addition to liches and other dark abominations that served the Jailer of the Damned, all brought back from death to help her destroy the world of the living, "Our dark and glorious Queen, what are your new orders?"
"It is time to bring us back to the main timeline, to claim my prize. Nozdormu, Murozond, Malygos, it is time to bridge the two timelines!" Sunset stated, as there wasn't much more for her to do in this world, not after slaughtering everyone with her army, where the dragons in question nodded their heads and started to gather their energies into the spell she had all of them create while the others wiped out the living.
The borders of Icecrown were surrounded by a barrier of arcane energy, the sign that someone was working hard to make her will a reality, before a surge of temporal energy started to gather as Chromie and her brethren began to bridge this world to the one she had been sent to not all that long ago. It was time to stop using this world as a hideout, so she could keep herself hidden until the time was right, and bring about the end of the living in her timeline, so she could focus on all of the potential threats that still existed, but had yet to reveal themselves to the stubborn heroes. Of course she couldn't just appear shortly after her disappearance, or even before that, hence why she had her allies steal the bodies of all those who fell defending Northrend from the Alliance and the Horde, to revive them and press them into service once more, and she even stole Naxxramas, which the living forgot about. That reminded her of the fact that, with all the time dragons on their side, there were now multiple necropolis' in the air as well, a sign of how massive their army was, though she knew all of them were stolen from the timelines her deceased alternate selves had come from.
As the dragons worked, and her army stood still, waiting for the gateway to open and link them up to the main timeline, she found herself thinking of the fact that she was about to fulfill her promise to those that prevented her from bringing the Lich King's will to reality, but in doing so they opened the doors for her to make her will a reality. When she took a bit of time to think about it she found it to be hilarious, as Tirion and everyone else assumed the Lich King stood above them all as the most dangerous being in the world, with the Dark Titan being even scarier than Arthas was, but they had made a mistake by not killing her when they had a chance. With all of her power, both new and old, Sunset stood as a force to be reckoned with, a being of darkness that wouldn't stop until all things bowed to her, regardless of who or what they were, and as she told Erith before she killed the dryad she wasn't just a being of death and destruction, she was becoming a being of domination. The dragon aspect was more due to her killing and raising the dragon Aspects into undeath, all while siphoning the anima from each of them, and what she had gained so far had made some interesting changes to her body, mostly in her tail for now, and she knew that if she kept it up she might become a true monster.
She had to admit that the idea of becoming a dragon of domination, which she envisioned to be a combination of all the powers of this world and the power of an alicorn, was an interesting one and that she might pursue it at some point after she completed her current goal, though her attention shifted back to what was in front of her as a dark light appeared in the air above them.
"Soldiers of the Scourge, the time has come for us to return to the main timeline and wreck havoc on the living, and those who dare to stand in our way." Sunset stated, where the army of undead cheered upon hearing that it was time to get her show on the road, as this was what she had been waiting for when she set this plan into motion, to which she nodded to Chromie, who shifted into her dragon form and let her climb onto her back, before they moved into the air, "It is time to make my will known to those who dare to oppose us! For the glory of the Scourge... and for the Lich Queen!"
The point in history that they would be returning at was right when Arthas fought the heroes on top of the citadel, which Nozdormu told her about while she was waiting for the Scourge to complete their mission, and sure enough she arrived in time to witness Frostmourne, Arthas' version, being shattered by Ashbringer, where the souls of the damned lashed out at him and knocked him to the ground, removing the helm from his head.
"Wow, what a battle." Sunset commented, where she noticed a force of heroes standing near Tirion, who had shattered her old master's blade with the stolen blade he carried, though they all stopped as they realized that she had returned, due to all of them knowing of her escape from the Violet Hold, but she focused and climbed off Chromie as she landed at what was the edge of the circular arena in front of the Frozen Throne, "I wish I could have gotten here sooner, but there were certain... obstacles... I had to overcome, and I am pleased to announce that my time in another timeline has come to an end."
"Sunset Shimmer, what do you want?" Tirion asked, though this was the worst case scenario for all of them, as the heroes were exhausted from their fight with Arthas, even if they had been slain and raised by the Light to finish this fight, while he had channeled a lot of his power to break Frostmourne, a blade that Sunset also carried he noticed, meaning they weren't ready for another fight, while their opponent clearly was.
"Many things." Sunset replied, where she shifted her stance for a moment as she raised her Frostmourne, calling forth the fragments of this world's version of the blade and absorbed them into her own, as per energy, which forced the souls of the damned to surge into her runeblade, before she weaved some of her magic into the air as she raised Arthas into undeath, his armor becoming the saronite plating she wore once upon a time.
"Of course she'd ruin our efforts, by reviving her dark master." one of the heroes, the orc death knight, remarked, though she did find that he had a runeblade that was an elegant axe that radiated all three aspects of their kind and seemed to be a counter to Frostmourne, no doubt made a reality by Darion and the rest of the Ebon Blade.
"Incorrect. I brought back a worthy soldier, so he could help spread death over this world." Sunset said, though after that was done she walked over to the base of the Frozen Throne and sheathed Frostmourne for now, allowing her to pick up her true prize, the Helm of Domination, though while it might not fit her head right now she knew a bit of remodeling would let it rest upon her head, "Congratulations, though, you beat the Lich King... and have paved the way for someone else to take his position as Master of the Scourge."
"That destiny is mine to bear." a rough voice replied, where they found a burned and charred figure, a human likely taken by the flames of a dragon and tortured by the forces of Icecrown Citadel, maybe even the Lich King himself, and he wore bits of saronite armor, like he had been in the middle of being remade into a minion of the Scourge, "I will take the Helm and become the Jailer of the Damned, to save..."
Sunset, instead of saying anything, shifted her spare hand and yanked the figure, who had to be Bolvar Fordragon, one of the paladins that Arthas wanted to torment to break Tirion, had the assault on Light's Hope Chapel failed, off of the Frozen Throne with her dark lasso, bringing him down to where everyone else stood, smashing him into the icy surface as a bit of punishment for his actions.
"You are also incorrect. The Helm of Domination belongs to me now." Sunset stated, where she raised the helm and let a smile appear on her face for a moment, as the heroes started to move and Chromie froze them where they stood, so they couldn't interfere with what was about to happen, before she claimed her prize.
As she lowered the helm onto her head, to claim the position that was now vacant due to Arthas being defeated in battle, a surge of magic washed over where she was standing and surrounded her, the magic on her armor altering the helm so it could match her body and not hurt her ears, even if she didn't feel pain anymore. The crystal section in the forehead area pushed forward, creating an opening for her horn to fit through with ease, while a pair of holes opened right on top so her ears could slip through without any problems, but other than that there was nothing else that needed to be altered. Once it rested on her head, and she lowered her hands, she felt a surge of power as she took her position as the Lich Queen, in addition to the Jailer of the Damned and all the titles that the mortals had given to Arthas and their predecessor, as there was one other before Arthas. In addition to that she felt a surge of power as a pair of leathery dragon wings, with the color matching her new tail, grew out of her back, replacing her cape in a matter of seconds, which faded away as if it no longer existed, and she flexed them with a smile on her face, where the force of her doing that knocked away the protective shell that had been covering her.
Such a thing allowed the heroes, Tirion, and Bolvar to see her once more, where she relished the looks of shock and terror that appeared on their faces, because now they knew that they weren't dealing with an ordinary undead knight, rather she was a being who would bring death to the world of the living.
Of course, with them being heroes and everything, many of them regained themselves as Chromie let them go, allowing all of the heroes to charge at her, where Sunset shifted her stance as she moved, swinging her weapon with lethal grace as her foes fell before her might. This showing caused the two paladins to back away from her, while Tirion held his weapon at the ready and Bolvar seemed unsure of what to make of this situation, though since neither seemed to be coming her way, and were studying her movements, she quickly dealt with the latter with a quick stab of her blade. Once Bolvar was down, however, she raised Frostmourne and pointed it at Tirion, who raised Ashbringer for a few seconds as he thought about the fact that her previous assault ended with the heroes, those who helped take down the Lich King, falling to her new dark might. In the following moment she zeroed in on her target and knocked the Light blessed blade out of the way, showing her foe that her strength was far more than what he was expecting when he heard she had disappeared from her cell, before she stabbed him in the chest, causing Tirion to cough up some blood in the process.
"I told you, Tirion, that you and the traitors would suffer, and so you will serve me in death." Sunset stated, where she let the Highlord perish on her blade before pulling it out of him, something that was followed by her channeling her power as she focused on all of the bodies that were around her, calling the heroes back to serve her as well, and it didn't take her all that long to force everyone there into undeath, "Now the fun begins! Rise and serve your ruler once more, servants of Icecrown Citadel, and bring death to this world!"
As she said that Sunset gathered the power of Death once more and stood in the center of the platform that was in front of the Frozen Throne, where she brought the runeblade down without wasting time and sent all of the power down into the citadel, rising the guardians of the massive structure and forcing them into service once more. Of course that meant a lot of things were happening at the same time, the living that were inside the structure were surprised by the sudden and unexpected revival of everyone who had fallen since the assault began, and that confusion was all her forces needed to begin the slaughter. As that happened her new soldiers descended down to the entrance of the citadel and assaulted their old allies, resulting in the deaths of several notable heroes, such as an orc called Saurfang and another one called Garrosh Hellscream, where her val'kyr ensured that they were brought back as soldiers of the Scourge. She also found that one of the flying vessels that had been attacking the citadel, a metallic ship with four propellers to lift it into the air, was fleeing, to get away from them, where Sunset had Chromie sneak aboard while she cleansed her domain and the rest of Icecrown of the living.
While her forces expelled the living from her domain, however, Sunset opened her new wings and found that, due to her blade's ability to steal powers and the memories of how to use those powers, she was able to fly with ease, allowing her to zero in on the Argent soldiers fleeing from the entrance, which was when her greatest surprise happened and her massive army from the conquered timeline warped in, slaughtering the living in a matter of seconds.
"Come, soldiers of the Scourge, let us lay waste to those defending Northrend." Sunset commanded, where she and her army marched out of where the citadel was located, while the necropolises started to spread out so they could cover the other provinces, meaning she was launching an attack on everyone who dared to attack her domain, though she swung her runeblade and cut through the Argent soldiers who dared to get in her way.
Tirion found that it was just like Sunset told him, and those she designated as her messengers to remind him, those who betrayed her were hunted down like dogs and slaughtered with the overwhelming might of the new Scourge she had put together in her time in whatever place she had spent her time in. Those like him, who stopped her from fulfilling the will of the Lich King, were slaughtered without a thought and raised without delay, forced to serve the one they had annoyed, all while he realized the dark truth that by doing that they had created a darker monster than what Arthas became. Sunset, in such a short period of time, had gained a level of power that was beyond what her former master had possessed and was now a force to be reckoned with, to the point where he had to wonder if anything in this world could stop her, when even the dragons had failed to kill her. Still, it pained him to fight against his former allies and kill them in her dark name, all so her val'kyr could raise the fallen Argent soldiers and press them into service as well, while she seemed to be having fun at his expense, not that he could resist her dark will, not with her wearing the Helm of Domination.
Sunset smiled as the Argent grounds were wiped out by Tirion, the heroes he had trained, and the soldiers that followed him into battle, allowing her forces to raise the fallen as servants of the Scourge, and with that done she turned her focus to the rest of the continent, knowing that it was only a matter of time until her army wiped out the rest of Northrend, then she could focus on the rest of what Azeroth had to offer her.
Twilight took a few steps back from the image that was on the crystal ball she had been using to connect with the spell on the mirror she had used to head to another world, all to get the Element of Magic back, as the scenes she had witnessed were hard to believe. Following her discussion with Celestia, about Sunset's supposed fate and what the Elements might have done to her, she decided to spend a great deal of her time moving the mirror from the Crystal Empire and having it transported to Ponyville, so she could conduct her research. Of course her mentor knew about her efforts, in fact she was the one who authorized the transfer of the mirror so Twilight could obtain it, even though Twilight knew there was only one reason behind Celestia helping her out, she wanted to know what happened to Sunset. The only downside to this was that she was constantly being interrupted by other adventures or troubles in Ponyville, but she dealt with them as quickly as she could so she could return to her search for the missing Equestrian, as she and Celestia refused to believe that the Elements had killed her.
For a while she thought that her efforts were going to be in vain, that no matter what she did she wasn't going to find her target, which made her realize that she was going to fail Celestia all over again, since her first true failure was being unable to save Sunset from what happened to her, to bring back the student her mentor trained all those years ago.
Then, as if spurred on by her failures, she made a breakthrough and discovered a world unlike the one she had followed Sunset to so she could recover the Element of Magic, full of types of magic she had never seen before and creatures she was interested in meeting as soon as she laid eyes on them. Unfortunately, while she wanted to study the world, Twilight had a task to focus on and tracked down Sunset as quickly as she could, finding that the lost Equestrian had landed in an interesting place, a frozen land that she thought was right outside the Crystal Empire, until she realized that it wasn't what she thought it was. The area was far too different from what was outside Cadance's domain, with massive cliffs and sheets of ice, along with an imposing and dreadful looking structure that looked like the citadel of the evilest creature that called the planet home, before her attention was brought to where Sunset landed. It appeared that Sunset had landed at what had to be the edge of a massive grave, as there was a massive undead skeletal dragon off in the distance, before she laid eyes on a being who stood above Sunset, in imposing armor and wielding an imposing sword that frightened her just by looking at it, before he stabbed her in the chest.
Twilight was sure that it had been the end of Sunset, that she had been sent to another world and was slain in no time at all, just like Spike told Celestia, but when she tried to find the world again she discovered something interesting, Sunset was alive, or maybe undead given the fact that her body color looked more drained than before, and it looked like she was being trained by some unholy soldiers.
The scene shifted to what had to be a few days later, where Sunset seemed dressed for war or something, given the blade in her hands, before she found the other Equestrian, who was in a mix of her human and pony forms, fighting beings and killing them with her weapon. It was a sickening sight to behold, blood being spilled, people dying by the dozens, the sky and ground darkening, and while all of that was going on, unless her eyes were deceiving her, Sunset was enjoying herself as she, well, slaughtered everyone in her path. Such a thing made Twilight wonder what sick horrors had been inflicted on Sunset to make her like this, as this wasn't the pony Celestia had trained before her departure to the other world, she refused to believe that this was Sunset, and she found that the horror continued as the figure slew everyone in her way, all while each person killed, in some way, was reborn into an unholy existence. Then came the assault on the beach, the point where she determined that something was seriously wrong, especially with how Sunset used her magic to wipe out everyone who stood in her way, all while her armor seemed to change every now and then, becoming a dark visage as she enforced her master's dark will over her enemies.
She could barely watch when Sunset, well, she couldn't really describe it, since she didn't have any knowledge of the dark arts, but it looked like she was torturing someone with her magic, extracting information from him, and after that she kept killing everyone in her path, like she was terror incarnate or something.
Eventually it came to the point where Sunset lead a force against a chapel and her force was defeated by a light of some kind, some force didn't want her to succeed, and yet, as many turned on the dark ruler, Sunset seemed convinced that her master was in the right and that everyone else was wrong. Twilight found that Sunset was sent to a prison and stayed in a cell for a long time, between four to five months based on her observations, before someone broke her out of it and sent her to some island with a mansion, which was when things started to get weird. She observed as Sunset went to war, not with the world she lived in, like one would expect after witnessing all of that, but rather she invaded other timelines with the aid of what Twilight guessed were time dragons, corrupt ones no less, and continued to slaughter everyone she came into contact with. What terrified her, more than anything else, was of Sunset gaining the power to force those who died to her blade to be reborn, meaning no one was safe from her dark might, especially when she claimed the terrifying blade that her old master wielded and the armor he wore, altered to match her new body.
She couldn't bare to watch as Sunset lead her army of the undead against the living, killing everything and everyone in her way like they were nothing, and realized that she couldn't tell Celestia what she had seen, it would break her heart to learn what Sunset was up to, yet she couldn't help but feel a sense of dread, like something bad was going to happen at some point in the future, and Twilight could only hope that this was one of those times where she was utterly wrong.