Naxxramas was a Naxxanar (Floating City) the Scourge attempted to build after acquiring knowledge and techniques from Azjol-Nerub.
Before Kel'Thuzad was killed by Arthas, he was sent by the Lich King Ner'zhul to Lordaeron to spread the plague, and Kel'Thuzad's personal vehicle was this Naxxanar (Floating City).
Furthermore, because Naxxramas was the first Naxxanar (Floating City) put into use by the Scourge and bore the heavy responsibility of overthrowing Lordaeron, it carried a large number of magical items, forbidden knowledge, and precious instruments.
Necromancy and death magic also belong to a branch of magic, so to go far enough on this path, research and experimentation are necessary.
Therefore, to attract more people to join the Scourge, Ner'zhul, with the Burning Legion's partial acceptance, created many expensive experimental instruments for him.
The undead plague originated from these inconspicuous bottles and jars—these terrifying viruses cultivated by magic could even corrupt the minds of the dead, and Arthas was well aware of their threat and importance.
The moment he replaced Ner'zhul and became the new Lich King, he unleashed his soul power to locate Naxxramas, but strangely, no undead in Naxxramas responded to his call.
This made Arthas realize that something must be wrong with Naxxramas; otherwise, such a large Naxxanar couldn't possibly have no undead capable of responding to his summons.
Therefore, resurrecting Kel'Thuzad was Arthas's idea from the beginning; he thought that this Necromancers, who once controlled Naxxramas, should have a special way to locate Naxxramas.
As expected, Kel'Thuzad had a unique way of sensing Naxxramas, but to Arthas's slight disappointment, even the Archlich couldn't get an accurate location.
The sea area north of Quel'Thalas?
This range was too vast; it was impossible to send people to search.
"The disappearance of Naxxramas must be related to those Dreadlords," Kel'Thuzad's hoarse voice sounded, "These demons also participated in the construction of the Naxxanar (Floating City); it's highly possible they have some backdoors."
"Currently, the only ones who know about the Scourge's existence and have reason to oppose us are those Dreadlords."
Kel'Thuzad bowed slightly, saluting Arthas, "Your Majesty, I might be able to help you solve this problem."
"You'd better be able to; tell me your thoughts first."
The Archlich nodded, respectfully replying, "Naxxramas's energy is not infinite; once the remaining energy can no longer support the Naxxanar (Floating City)'s flight, the Dreadlords will have to force Naxxramas to land somewhere."
"We can't know where the Dreadlords will choose to land, but... we can lure him to land somewhere."
Kel'Thuzad casually imprisoned a lost soul; this soul had lost its self-awareness over a long time, and the Archlich's bony hand tightly gripped it, condensing the soul into a crystal in the cold air.
"Naxxramas's power source is souls; if the Dreadlords still want to maintain control over Naxxramas instead of escaping alone, he will definitely find a place to replenish its power."
Souls?
Kel'Thuzad's words inspired Arthas: Icecrown Glacier had the most lost souls attracted by the entrance to the Shadowlands, and most of these specters had lost themselves in the material world.
Their consciousness had long dissipated, leaving only forms condensed from soul energy wandering in the material world.
Perhaps he could find a way to capture some of these souls and make them appear to be gathered in one place.
In this way, whoever was eager to replenish Naxxramas's power would surely find this place, and then Arthas would know who was piloting the current Naxxanar (Floating City).
If it really was the Dreadlords... perhaps he could glean a lot of desired information from him.
...
Just as Arthas was finding clues about the Dreadlords, in an ancient ruin in Kalimdor, an orc with eerie green glowing eyes moved through the broken buildings, holding a torch.
Suddenly, the orc stopped, frowned, leaned on a broken stone pillar, and whispered.
"I hear you, Detheroc! You stay in Naxxramas; you can't let that Naxxanar (Floating City) fall into the hands of the current Lich King!"
"Enough! Do you think Mal'Ganis didn't die miserably enough? Infiltrating a fully developed Dalaran now is undoubtedly giving those human mages a chance to catch us."
The orc's neck twisted for a moment, then quickly returned to normal, but the strange movements of his body clearly indicated that he was no longer alive but a controlled puppet.
His voice held a hint of anger; he sounded very displeased, "Do you think my job here is easy? This is the territory of those damned Kaldorei, and with the Legion not yet arrived, it's impossible for just a few of us to conquer this planet."
After speaking, the orc cut off contact with the other Dreadlords, but he still didn't remove his disguise: he was now acting alone, hoping to find something useful in the ruins of the ancient elven empire.
That new Lich King was truly too bizarre; he silently took out Mal'Ganis and Ner'zhul before the other Dreadlords could react.
Mal'Ganis had been missing for a long time; originally, the other Dreadlords thought he was faking his death, wanting to have some fun on Azeroth, but now it seems... he was very likely truly sent back to the Twisting Nether.
Of course, there was an even worse guess, but Detheroc confirmed that Mal'Ganis was "killed" by Frostmourne, so Mal'Ganis absolutely should not have had his soul bound by that demonic sword.
There was a long-standing rule among the Nathrezim: Dreadlords cannot harm each other, including the weapons and items they create, which also cannot cause harm to other Dreadlords.
This half-curse, half-rule spell would entwine itself around every Nathrezim. Frostmourne was a demonic sword forged by the Nathrezim and Kil'jaeden together; logically, this sword should absolutely not be used to kill Dreadlords...
Unless... the curse on the sword was removed.
Almost all the Dreadlords didn't think in this direction, because for countless millennia, no one had ever been able to break this ironclad rule—however, they didn't know, and couldn't have guessed, that the power Arthas could wield reached the very source of the universe.
But all in all, Mal'Ganis's disappearance still made the Dreadlords extremely cautious; they decisively abandoned the Scourge and prepared to find another way to summon the Legion.
By then, it wouldn't be too late to settle accounts with Arthas...