As they swiftly assumed their designated roles, the disciples stood poised to enact Xue Xinyu's stratagem. They moved with a newfound purpose, their actions synchronising in a seamless ballet of defence and attack, each one complementing the other like notes in a perfectly orchestrated symphony.

"And what of me, Shizun?" inquired Liang Zhiguan, stepping forward with a look of earnest determination. He was like a knight ready to ride into battle, eager to play his part in the unfolding drama.

"Remain steadfast in the centre, ensuring none breach our defences. The rest falls to me," Xue Xinyu declared, retrieving something from his voluminous robes with the air of a magician about to unveil a trick. It was the infinity bag, a seemingly unremarkable pouch that, in reality, concealed a vast array of magical paraphernalia from prying eyes.

From the depths of this mysterious bag, he pulled forth a small, smooth stone, which seemed to shimmer with an inner light. Advancing toward Liang Zhiguan, he extended it to him with a solemn expression. "Hold onto this for the moment," he instructed, his tone leaving no room for questions.

"What is it?" queried Liang Zhiguan, his curiosity piqued by the enigmatic object now resting in his palm. It felt warm to the touch, pulsating with a gentle rhythm like a tiny, contented heartbeat.

"All will become clear shortly," replied Xue Xinyu as the barrier began to wane, its shimmering surface flickering like a candle in the wind. His eyes flickered with a hint of mischief, suggesting that whatever revelation was to come, it would be anything but ordinary.

Meanwhile, Lánjiàn, the ever-loyal sword, continued its relentless assault upon the encroaching monsters. It moved with a deadly grace, slicing through the ranks of the grotesque creatures with a precision that left their foul-smelling entrails scattered across the ground.

With the barrier fully dissipated, the creatures surged forward once more, their grotesque forms surging like a dark, malevolent tide. The disciples, undeterred, redoubled their efforts, coordinating their actions with a fluidity that spoke of their training and resolve. They moved like a single entity, each one fulfilling their role with a precision that was almost mechanical in its efficiency.

"Master Xue, our defences are faltering. My qi is nearly spent," Junjie reported, his voice tinged with exhaustion. Sweat dripped down his forehead, and his hands trembled from the exertion of maintaining his attacks.

Recalling Lánjiàn to his side with a mere thought, Xue Xinyu withdrew a talisman from the infinity bag, affixing it to the blade with a deft motion. Instantly, the sword shimmered and replicated itself several times, the multiple iterations carving through the ranks of monsters with renewed vigour. It was as if the sword had multiplied its fury, each copy moving with the same lethal elegance as the original, turning the battlefield into a whirling dervish of deadly steel.

"Alright, listen up!" Xue Xinyu's voice cut through the cacophony like a bell. "We're not out of the woods yet, but we have the upper hand. Keep those monsters at bay and stick to your roles. And remember, we're not just fighting for ourselves; we're fighting for everyone back home."

The disciples nodded, their faces set with grim determination. They were ready to face whatever new challenge awaited them in the darkness beyond, each one resolved to hold their ground and protect their comrades, no matter the cost.

"Zhiguan, raise the stone aloft," commanded Xue Xinyu, his voice resonating with an authority that brooked no dissent. He stood tall and imposing, his robes fluttering like a banner in the breeze, as if daring the very forces of darkness to challenge his command. Following the directive with a mix of apprehension and trust, Liang Zhiguan elevated the stone above his head. Instantly, the stone burst into a radiant azure hue, glowing with an intensity that outshone the sun at midday.

"What in the world is happening?!" exclaimed one of the disciples, his voice tinged with a mixture of awe and bewilderment as the brilliant light washed over them.

"It's like it's giving me energy!" marvelled Junjie, his eyes widening as he felt a rush of vitality coursing through his veins. He flexed his fingers, feeling the surge of qi renewing his strength and banishing the fatigue that had weighed him down moments before.

The light from the stone streamed forth like a river of pure power, infusing each disciple with a newfound vigor. It was as if the very essence of life was being poured into them, filling their bodies with a boundless energy that erased their weariness and fortified their spirits. The disciples stood taller, their eyes gleaming with renewed determination.

"It shares my qi with you all, for even I alone cannot vanquish them," Xue Xinyu elucidated, his tone calm but carrying an undercurrent of steely resolve. He glanced at each disciple in turn, his gaze lingering just long enough to convey his unspoken confidence in their abilities.

The revelation left the disciples stunned, their mouths agape and eyes wide. Who could possess a reservoir of qi so vast that it could be dispensed with such liberality? The question hung in the air, heavy with disbelief and awe. They had always known Xue Xinyu to be powerful, but this display of magnanimous strength surpassed anything they had ever imagined.

Xue Xinyu himself remained uncertain about the full extent of his own qi cores. They were a mystery even to him, a reservoir of power that seemed almost bottomless. He was wary of delving too deeply into their nature, lest he expose the demonic essence that lay hidden within him. Yet, driven by necessity and a fierce determination to protect his disciples, he employed every method at his disposal to overcome the overwhelming horde of monsters. He had no clear strategy, but his resolve to prevail was unwavering, like a rock standing firm against a tempest.

"We don't need to kill them all," Xue Xinyu said, his voice cutting through the noise of battle like a knife through butter. "Just enough to buy us time to escape." He paused, scanning the faces of his disciples. "Can all of you fly swords?" he asked, his eyes narrowing as he assessed their capabilities.

After a series of vigorous nods confirmed that everyone could indeed fly on their swords, he began to formulate a plan for their swift departure. "Zhiguan, in a few seconds, I'll create an opportunity for you all to leave. Take them to the big mountain you flew by earlier. I'll follow later," Xue Xinyu instructed, his tone brooking no argument.

"But, Shizun—" Liang Zhiguan began to protest, his face a mask of concern and loyalty. However, he fell silent as Xue Xinyu fixed him with a stern look, a look that spoke volumes. It was a look that said, "Trust me," and "There is no time for debate." Nodding reluctantly, Liang Zhiguan quickly put the stone into his robe, the precious artefact disappearing into the folds of his clothing.

As the undead creatures surged towards Xue Xinyu like a tidal wave of malevolence, Liang Zhiguan led the others away, his heart heavy with the knowledge that he was leaving his master behind. He glanced back one more time, his eyes lingering on Xue Xinyu's solitary figure, before turning his attention to guiding the others to the safety of the mountain. He was determined to get them there safely, even if he couldn't help Xue Xinyu directly.

Amid the chaos, a revelation dawned upon Xue Xinyu, an epiphany so glaringly obvious that he almost laughed at his previous oversight: undead creatures were, by definition, deceased. Corpses. And with this realisation came a newfound strategy—a way to turn the very nature of his enemies against them. Despite the overwhelming odds and the countless creatures swarming towards him, Xue Xinyu knew he had found a way to seize control.

Recalling Lánjiàn to his side with a flick of his wrist, he caused the spectral duplicates of the sword to dissipate into nothingness, their lethal energy evaporating like mist in the morning sun. He held the sword aloft, its blade gleaming with an otherworldly light.

"Zalak'thul durvok'ash," he intoned, his voice taking on a deep, resonant quality that seemed to echo from the very depths of the earth. His eyes blazed with an intensified azure radiance, a light that pierced the darkness and illuminated the battlefield. In response, the monsters' eyes flickered with a darkened hue, a malevolent glow that hinted at the dark forces he was now commanding.

The creatures halted in their tracks, their movements stuttering to a stop as if some unseen hand had seized control of their bodies. They stood there, frozen, their grotesque forms illuminated by the eerie glow of Xue Xinyu's eyes, compelled to heed his command. The air crackled with energy, the tension thick enough to cut with a knife.

With a commanding sweep of his arm, Xue Xinyu directed the undead horde to turn on each other, their eyes flickering with confusion and reluctant obedience. They began to tear into their own ranks, a chaotic melee of claws and fangs, their darkened forms writhing and contorting as they fought amongst themselves. The battlefield, which moments before had been a scene of desperate struggle, was now a writhing mass of self-destruction, the creatures' malevolent energy turned inward.

Surveying the sprawling undead horde that stretched out before him like a sea of writhing limbs and gnashing teeth, Xue Xinyu's keen eyes honed in on the larger specimens. These creatures, towering over their lesser kin, often harbored cores—those pulsating, arcane orbs within their grotesque forms—that held considerable value or utility.

With a flick of his wrist, Lánjiàn danced through the air with the precision of a surgeon's scalpel, its blade shimmering with an otherworldly light as it sliced through the ranks of monsters. Each strike was deliberate, calculated, aimed not just to slay but to retrieve. And as the monstrous bodies fell in its wake, their cores tumbled to the ground with a sickening squelch.

Employing a technique that would have made even the most seasoned warlocks envious, Xue Xinyu deftly drew forth the demonic qi contained within these cores. It was a delicate manipulation, akin to coaxing fire from ice or water from stone, requiring finesse and a deep understanding of the dark arts. The qi flowed into his grasp like a torrent, its malevolent energy mingling with his own, infusing him with power that surged through his veins like liquid fire.

Yet, with every influx of energy, Xue Xinyu couldn't ignore the discomfiting sensation that accompanied it—a tangible expansion of his demonic core. It was an unsettling feeling, akin to a serpent coiling within his chest, its scales brushing against his soul. But for all its unpleasantness, this expansion was indispensable for the task at hand.