Invisibility Art was already an exceptionally rare spell, and it was Lei Dong's absolute favorite—the ultimate method for ambushing enemies, and wickedly paired with the Ghostly Strike. This combination had turned this creature, named Ghostly Grunt, into a tyrant of the darkness, a nightmare for its foes. Furthermore, being a High-grade Grunt, it surpassed Mid-grade Grunts in both agility and intelligence.

As for the Top-grade Grunts, they held yet another superiority. Regrettably, estimating by the previous promotion patterns, the time required to capture enough ghosts to upgrade even one Top-grade Grunt would take Lei Dong at least three years, even under the most favorable conditions. Perhaps later, when he reached the Foundation Establishment stage and enjoyed a longer lifespan, he could indulge in such pursuits. But for now, it was simply a waste of life.

If he didn't seize his youth, when his physical functions were at their peak, to advance to the Foundation Establishment stage sooner, promotion would become increasingly difficult with age. Moreover, a single Top-grade Grunt was significantly inferior in overall power compared to three cooperating High-grade Grunts. Therefore, balancing time constraints against efficiency in strength enhancement, refining three High-grade Grunts was currently the most cost-effective endeavor.

Aside from these three High-grade Grunts, another gain for Lei Dong was the successful refinement of the High-grade Myriad Ghost Banner. Although called a Myriad Ghost Banner, in reality, given Lei Dong's current cultivation, he could at most refine a mere hundred or so low-level ghosts, reaching the realm of a Hundred Ghosts Eruption. To command ten thousand vengeful spirits, given his current spiritual sense strength, would be utterly impossible to suppress; like the Evil Ghost Veil, it would almost certainly result in a violent backlash.

The Myriad Ghost Banner was a magical artifact that prioritized the quantity of souls over their quality. Using spiritual ghosts for refinement was a monumental waste. Of course, utilizing wild grunts, cultivator souls, or beast souls was also possible, but it was completely different from a Natal Ghost Servant. All souls refined by the Myriad Ghost Banner would ultimately unify into a single, black, misty, primordial ghost state. Naturally, there would still be variations in strength among these misty ghosts.

However, the inherent limitation of the Myriad Ghost Banner lay in the total power a cultivator could command. This capacity depended on the banner's quality and the user's cultivation strength. Cultivators who favored using the Myriad Ghost Banner had gradually coined a name for this index of manageable ghosts: Soul Power Limit Value, or 'Soul Value' for short.

The so-called Soul Power Limit Value referred to the critical threshold of the maximum total strength of ghosts a cultivator could suppress, calculated by combining the user's spiritual sense strength with the bonus provided by the banner's quality. For instance, if Lei Dong's current suppression power was one hundred, this High-grade Myriad Ghost Banner might boost it to about one hundred and fifty. Calculating one ghost refined from an ordinary vengeful spirit as one point, his banner could suppress, at most, one hundred and fifty of the lowest-grade ghosts. But if a ghost refined from a Grade One Wild Grunt (rated at ten points) was considered, he could only command fifteen Grade One ghosts. Higher grades required additional points: every subsequent level consumed an extra ten points. Thus, a ghost refined from a Grade Twelve Grunt would cost one hundred and twenty points each. This implied that, given Lei Dong's current power, he could suppress at most one Grade Twelve ghost within the banner, plus some weaker ones. Naturally, this was merely a rough estimate, as the specifics involved significant fluctuation.

In fact, the power calculation for ghosts within the Myriad Ghost Banner differed greatly from the individual combat power of the Grunts. Those ghosts were genuine masses of black mist acting purely on instinct and command. Their so-called 'grade' merely referred to the inherent strength of their soul essence. Indeed, a Grade Twelve Ghost was significantly stronger than low-grade ghosts, its pure soul strength equivalent to roughly one hundred and twenty low-grade ghosts. But this absolutely did not mean a Grade Twelve Ghost could defeat one hundred and twenty low-grade ghosts in a one-on-one engagement. Quite the contrary: due to differences in attack methods and intelligence, the numerically superior one hundred and twenty low-grade ghosts could often wear down a Grade Twelve Ghost.

This contrast in strength was astonishing when compared across cultivators, demonic beasts, and Grunts. After all, a Grade Twelve Grunt could relatively easily defeat over a hundred ordinary vengeful spirits. Similarly, a cultivator at the twelfth level of Qi Refining could easily subdue more than a hundred robust mortal soldiers.

But ghosts, even low-grade ones, were uniquely special. They differed from vengeful spirits, fierce beasts, and mortal soldiers. Their forms were all black mist; their attacks often manifested like swarms, achieving tremendous power once they scaled up into an overwhelming tide.

Naturally, trying to defeat a twelfth-level Qi Refining cultivator with just over a hundred low-grade ghosts was pure fantasy. This was because a twelfth-level cultivator was far more sophisticated than a Grade Twelve Ghost; the cultivator possessed various spells, magical artifacts, talismans, and so forth. The Grade Twelve Ghost, however, only possessed near-equivalent soul power—devoid of spells, equipment, physical bodies, or intelligence. However, if the number of low-grade ghosts swelled to the thousands, they would pose a significant threat to a twelfth-level cultivator. The might generated by sheer scale was no joke; one only needed to consider the power of a massive ant colony.

Hence, Natal Ghost Servants pursued individual power—the more supreme the Servant, the better. Conversely, the ghosts in the Myriad Ghost Banner were better off being lower-grade to maximize the scale effect. Tens of thousands of low-grade ghosts blotting out the sky, attacking with density surpassing locusts—the imposing force of that assault was easy to imagine.

However, continuously refining the banner using a large number of Inferior-grade vengeful spirits into low-grade ghosts carried a drawback. If they encountered a difficult battle, the sacrifice rate among the banner's ghosts would be immense because those low-grade spirits died too easily, necessitating constant refinement to replenish the losses. If the ghost count couldn't keep up, the banner's power would drastically diminish. Conversely, using slightly stronger ghosts made them far less susceptible to immediate death.

In summary, refining the Myriad Ghost Banner with low-grade or high-grade souls each had its distinct advantages and disadvantages. The former unleashes the banner's maximum potential but suffers excessive attrition in fierce combat. The latter drastically reduces losses but falls far short in terms of raw power compared to low-grade spirits. The final judgment of which is superior rested entirely on the Myriad Ghost Banner owner's own calculation.

But since Lei Dong needed to feed his High-grade Grunts, he typically let the Grunts devour most of the wild grunts or low-level demonic beasts he encountered. This left him with only one practical choice: utilizing vast quantities of common vengeful spirits, reserving only about a dozen more advanced ghosts specifically to serve as the main souls within the Myriad Ghost Banner. Otherwise, almost all others were Inferior-grade.

With the Hundred Ghosts Eruption formation complemented by the cutting-edge combat strength of his Natal Ghost Servants, their combined power should multiply exponentially. However, Lei Dong had not yet tested this in actual combat to gauge the true effect.

The Myriad Ghost Cave, situated in Yin Wind Canyon, one of the notorious dangerous locales.

Lei Dong was currently wrestling with a Grade Seven Wild Grunt.

"Boom~"

The Wild Grunt, clutched tightly by the Nether Ghost Claw, didn't even manage to struggle free before being brutally torn apart by three High-grade Grunts, whose ranks were not yet overly high. Joyfully, they quickly devoured the soul fragments lingering in the air. After this division, the three Grunts each solidified and strengthened considerably. The Ghostly Grunt, which was mid-to-high Grade Three, even directly advanced to Grade Four.

Indeed, Grunts refined from High-grade spiritual ghosts possessed a terrifyingly fast rate of improvement. For Lei Dong, the faster the Grunts improved, the better. He wished secretly that the three High-grade Grunts he was laboriously cultivating could instantly ascend to the level of Ghost Guards. Of course, that was mere fantasy; even a Celestial Spirit Ghost could not achieve such a rate of promotion.

Because of the excellent performance displayed by these three High-grade Grunts, Lei Dong found himself increasingly fond of them; their fierce and savage appearance seemed rather endearing in his eyes.

Just as he spread his divine sense outward to scout for the next Wild Grunt, he suddenly spotted a faint greenish streak of light approaching rapidly from the distance in the sky. The light streak moved like a meteor, leaving a long fiery tail, quite spectacular to behold.

Lei Dong’s heart tightened slightly. Judging by the speed of the light streak, it was likely a High-grade flying artifact. Anyone who could afford a High-grade flying artifact was certainly no pauper. He immediately, without showing any reaction, recalled the three still lower-ranked High-grade Grunts. He released the Mid-grade Shadow Grunt, ordering it to conceal itself nearby, while simultaneously gripping several Yin Fiend Lightning Pills hidden in his hand.