What if someone's transmigrated into Gu world, along with the Library of Heaven's Path?
By this world's logic, the Library would be his Vital Gu.
Library of Heaven's Path is like an overpowered version of the Rank Nine Wisdom Gu. It can deduce the information and flaws of someone executing their battle moves. It can do the same to objects via touch.
As the Library 'powered-up', he can even deduce and collect things with a glance.
While normal Gu needs feeding, the Library can make do without. It can 'evolve' as the user collects more and more knowledge.
It can contain any written information, such as manuals, recipes, and insights, which the user can access with a thought. His reading speed would be many times faster this way.
With a sufficient amount, he can acquire the perfect version of each discipline. Among those of same cultivation level and attainment, he's undefeatable.
He could even hold his own against those of higher levels without relying on the Library.
The utilization of Library made him able to utilize his Gu most effectively; targeting the fatal weakness of his opponents.
It's also virtually undetected among all beings in the Gu World.
Unlike Wisdom Gu, the Library cannot provide inspiration and directly answer questions. However, it could directly deduce flaws in every single idea thought up by the user.
With that, it's a lot simpler to deduce many things by eliminating the impossible. The user can perfect any single remnant Gu Recipes as long he had a large number of similar recipes and corresponding manuals.
The same goes with Killer Moves.
The Gu Refinement process would be perfect as long the one refining followed his instructions step-by-step
The Library grants the user an incredibly pure Primeval Essence (zhenqi) and it's also attribute-less.
It can instantly heal the user, turn into deadly poison, able to subdue Gu Masters of higher cultivation, and change attributes to lightning, fire, ice, and so forth.
The lack of attribute also made concealing traces easier.
With its pureness, the user can activate Gu with a lot less Primeval Essence, yielding better results compared to average Gu Master.
All in all, the Library is the deadliest counter to Wisdom Path Gu Masters. No matter how strong they are, they would be dead meat upon deducing the user.
Against Soul Path Gu Masters, his soul is extremely resilient. To temper his soul, there's no need for Dong Hun Mountain or Luo Po Valley--he can cultivate the perfect Soul Path, or gain gratitude from his students to form a Golden Page.
Which he can use to temper his soul, launch a deadly attack that could even disable a Gu Immortal, instantly assimilate the entire library's knowledge, and seal any artifact (or Gu). Its other function is bloodline purification, but its application is unsure in the Gu World since bloodlines didn't matter as much (with the exception 'bout Blood Skull Gu). It's mostly 'but the Gu Master's aptitude and talent in certain paths.
He can use his Primeval Essence (or Immortal Essence) to induce a cultivation breakthrough for his tamed beasts and temper their strength, which could be even stronger than him in cultivation level.
While beasts can only be as strong as Immemoral Desolate Beasts, with his immortal essence, he probably could push them into the Venerable rank, defying the Heavens.
It's also the perfect nourishment for Spirit Herbs and all kinds of plants and natural resources. Making them recover in a blink of an eye.
With the infusion of true meaning, dream realms, and inheritance, it is possible for the Library to infuse experiences to the Library's user. Making him accumulate battle experience, and expertise in Gu Refinement, Weapon Forging, Formations and such.
In the original story, in the Master Teacher Continent, it's not possible to directly improve one's practical expertise without years of practice, but in Gu World, it's possible through things listed above.
Plus, without the Innate Fetal Poison, the MC has all the time to learn what he wanted.
It could also form a more perfect version of these inheritances as long the quantity was enough or it was compiled with the vast majority of similar path manuals...
The only drawback--the expenditure for his cultivation is costly. But it would only deter the user when he's still a Gu Mortal.
As for talent and aptitude, it's meaningless for him. As long he had enough manuals and primeval stones, he could even push to rank five peak stage in one go.
When he becomes a Gu Immortal, just the Tribulations alone were enough to fuel his cultivation. Although due to its need for pure essence, the tribulations need to be of a catastrophic scale to advance the same pace as others.
With this alone, the Library could be considered a Rank Ten Wisdom Path Gu, that also encompass many other paths.
The moment he becomes a Gu Immortal, his blessed land could accommodate many kinds of Dao Marks and able to cultivate any path he wants. Its size would be boundless as Heaven and Earth.
Due to its unique Heaven Dao Mark, the calamities would be a lot more nourishing the blessed land, no matter how severe it was.
Activation of Immortal Gu would cost a lot less and having bigger outputs. As a drawback, one immortal essence stones cannot fully recover a bead of green grape immortal essence.
As he came from the outside world, he's considered an Otherworldly Demon.
Thus, Heaven's Will and the Fate Gu cannot control him. Despite his body belonging to a native, the Heaven's Path Gu practically disables their manipulation.
It also meant he's liable for Red Lotus and Thieving Heaven Demon Venerable's True Inheritance.
Thieving Heaven's killer move, Divine Concealment, and Ghostly Concealment would be redundant, as the Library already possess the ultimate counter for deductions.
Despite his overpowered abilities, by the time he started, he'd still be a nobody with only rank 1 cultivation stage.
It's best for him to lay low and develop his abilities at a steady pace, concealing his abilities unless necessary.
If his abilities were known, he would be hunted by the Gu Masters, even for his Otherworldly Demon status alone.
...and since the Library of Heaven's Path came from a different Heaven from Gu Master world, the Heavenly Court and the Heaven's Will might make life difficult for him.
...but due to his counter-deduction abilities, unless he made a ripple big enough to be noticed with the naked eye, he should be safe as long he's still a Gu Mortal.
As the way to power up involves doing a good deed to people (his students), he's probably better suited for the righteous path. But if the true nature of his ability were known, everyone would try to control him.
Like in the original novel, it may be a good thing to pretend to be behind a super force (Yang shi) as a failsafe.
...when everything else fails, let's remember that the MC has thick plot armor.
