(Here I will write down some key concepts and their explanation. I will also add the mc's abilities to help readers remember them—but only the ones we've seen so far.)
-Martial Pressure: A formless energy field released by a warrior's flesh and blood. Martial Pressure can overwhelm, paralyze or outright destroy anyone unable to resist it. Its intensity depends on the warrior's body cultivation level and Martial Depth.
-Martial Depth: The conceptualization of a warrior's battle-prowess when compared to other warriors of the same realm. Influenced by the warrior's constitution, cultivation methods, bloodline and the likes; the deeper the Martial Depth, the greater the warrior's battle-prowess when compared to other warriors of the same level. But in general, deeper Martial Depth also means stronger tribulations and greater energy requirements for breakthroughs.
-Blood Energy: The energy contained in all corporeal beings' flesh and blood. Blood Energy not only powers all physical feats, but is also the driving force behind martial skills.
Note that, due to the environment they evolved in, and the Primordial Essence they had access to, the Blood Energy of primordial entities is a lot more dense and potent than the warriors of the Divine Age.
-Primordial Essence: The "air" of the Primordial Era. By breathing Primordial Essence for extended periods of time, primordials naturally gained stronger constitutions and Blood Energy than the people of the Divine Age.
-Spiritual Energy: The energy hidden in all souls, and the force powering Spiritual Powers and Mantras. No matter how weak or ordinary, all people possess at least one unit of Spiritual Energy. But without Spiritual Power to channel it, Spiritual Energy is useless.
-Spiritual Power: Innate spiritual abilities that one has to be born with. Without Spiritual Powers, stepping on the spiritual path and learning mantras is impossible. Spiritual Powers also determine the type of mantras that their owner can learn.
For example, Huan Yi's Eye of Slaughter and Eye of Dancing Devils are both Spiritual Powers. The Eye of Revelation is also a Spiritual Power.
-Mantras: Spells cast by channeling and manipulating Spiritual Energy through chants and mudras. The mantras that a Spiritual Master can learn entirely depend on their Spiritual Powers. And so because Huan Yi possesses the largest panel of Spiritual Powers, he can learn virtually all mantras.
-Blood Manifestation: Proof that a warrior has cultivated their bloodline to the peak, enabling them to obtain a new transformation, with vastly superior physical abilities and new bloodline skills. In the Primordial Era, the Blood Manifestation wasn't rare. But in the Divine Age, it has become a skill reserved for the elite of the Three Realms.
Note that as the Paragon of all Infernal Powers, Huan Yi can use the Bloodline Abilities and Blood Manifestations of other Infernal-blooded folks with infinitely more power and skill.
-Spiritual Anima: Even rarer than the Blood Manifestation, the Anima is proof that a Spiritual Master has cultivated their soul to the peak, enabling them to cast a projection of their soul. That projection can work independently from the caster, control overwhelming domain-type abilities, and cooperate with the caster to unleash unique mantras and Spiritual Powers that no one else should be able to copy.
But due to his status as Sin-Born Overlord and Tyrant Lord of Karma, Huan Yi is the exception to that rule, able to use the Animas of all Demons, Banes, or Sins.
Note that even the unique spiritual abilities developed by infernal-blooded folks can be robbed by Huan Yi without ever meeting them. This also means that attempting to harm or defeat Huan Yi with infernal powers is simply impossible.
-Karmic Flux: An energy source born from the Karmic Connections between all lifeforms. Only individuals with high levels of Karmic Control can accumulate Karmic Flux, using it as an extra power source for their various abilities. A lot more versatile and powerful than Spiritual Energy, in the hands of a master, Karmic Flux has many applications such as establishing connections with the enemy, making them see their opponent as close kin, or slowly reducing their willpower. But Huan Yi prefers smashing his foes in the old-fashioned way.
-Transcendent Principles: Starting with the Path Seeker level, warriors and spiritual masters can connect to the Elementary Principles and channel their powers into their bodies. Perfected Warriors can connect to the Higher Principles, and Ninefold Transcendent can start channeling the Transcendent Principles.
But in truth, 99.999% of the Three Realms' cultivation world never goes beyond the Elementary Principles. The difficulty of mastering Higher Principles or above is just that obscene.
And even among Transcendent Principles, there is a hierarchy:
Man Transcendent (Karma, Samsara, Hexes) <> World Transcendent (Fate, Rules, Chaos) <> Thearchy Transcendent (Cause and Effects).
Note: There are more Transcendent Principles that we will discover along the way. We have also not properly introduced the Power of Hexes yet, but since it will be important moving forward, I'm putting it here.
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Huan Yi's Abilities (as a multi-bloodline Paragon and the most accomplished warrior in the history of the Three Realms, Huan Yi has the most abilities of all—abilities that we can't possibly list fully here. I will focus on the recurrent ones and gloss over the rest):
-All abilities of the infernal clans.
-All abilities of Karmic Spirits (including Karmic Fire, Karmic Lightning, and Karmic Dissociation).
-Eye of Slaughter: Huan Yi's right eye. Can accumulate the Powers of Destruction (typically only available to Martial Overlords) and Death. This eye also possesses the unique ability to connect to the Myriad Abysses and summon the Beasts of Annihilation. But only Huan Yi can see them.
-Eye of Dancing Devils: Huan Yi's left eye. Can manipulate his targets into embracing their deepest emotions and desires, trick them into Demonic Pacts, or cause demonic mutations/transformations. This Eye also accumulates Evil Qi.
-Eye of Revelation: Stolen from Wen Tianhua and perfected to match Huan Yi's body. Grants perfect peripherical vision across at least 100 miles and the ability to see through various concealments. It can also project into the distance, analyze the opponent's fighting pattern to foresee their movements, detect treasures, or perform minor divination tricks.
Only the descendants of Heaven's imperial line and the Shi Immortal race can use the Eye of Revelation.
Spiritual Energy pretty much decides the eye's limits. For example, Taiwei's Eye of Revelation could improve his speed and reflexes to match and avoid his enemy's attacks. But he didn't have enough Spiritual Energy to improve his speed and reflexes to match Taotie's Limit Break.
Note that Shiyuan possesses the strongest Eye of Revelation, even more powerful than Huan Yi's (at least at the moment). But Shiyuan often loans his eye to Daode to assist his brother's deduction abilities.
-Evil Eye of Tyranny: A forbidden ability created by Huan Yi and sealed in the Manuscript of Forbidden Secrets. This eye can mark the opponent with a Tyrant Seal, enabling Huan Yi to suppress their five senses and seal one of their abilities (typically the one he finds most troublesome). It also erases the opponent's pain tolerance while multiplying their sensitivity.
Note that the Tyrant Seal doesn't work on Transcendent Principles, but will not vanish even if the eye is destroyed.
-Collapsing Hands of the Sinful Paragon: According to the Guardian, the strongest martial skill that Huan Yi can use without the Black Dragon Spear. Relies on the polarity of Yin and Yang, Huan Yi's evil powers, and his bloodline abilities to summon a demon-buddha hybrid statue that traps the enemy with one thousand virtuous and demonic palm strikes.
This martial skill can also channel Huan Yi's evil karma, turning it into a spiritual weapon to bombard his enemy's soul.
-Paragon Consuming Art: Created for Taotie to speed up her cultivation and battle-prowess growth. The strongest devouring ability. And once paired with Taotie or Huan Yi's innate devouring powers, enables them to consume virtually anything.
-Five Fingers Deathblow: A legendary martial skill invented by none other than Huan Yi—contains the powers of destruction and death. In the Primordial Era, there was a saying that once the five fingers fell, all lives were doomed to extinction.
-The Five Forbidden Gates (Forbidden Might, Cursed Celerity, Demented Will, Forbidden Pleasure, plus one final gate that we haven't seen yet): The result of cultivating the Manuscript of Forbidden Secrets as one supreme technique. The gates' powers are self-explanatory, individually providing extreme strength, speed, toughness, pleasure and one last that we haven't seen yet.
-Zero Karma: One of the abilities developed by Huan Yi after becoming the Tyrant Lord of Karma. Can freeze the Karma of an entire world, basically giving Huan Yi the power to completely stop the flow of time.
-Karmic Deduction: One of the abilities developed by Huan Yi after becoming the Tyrant Lord of Karma.
As overpowered as the potential of the one it's used on, by relying on all available information about Huan Yi's body, bloodline, eating habits, hobbies, cultivation speed, and the like, the Karmic Deduction can predict what form, abilities and cultivation he will possess in the years to come, draining his Karmic Flux to temporarily give him that form and powers.
This ability is extremely demanding in Karmic Flux, and could automatically bring Huan Yi's reserves to zero if he did something crazy like trying to project himself 100 years into the future.
Note that Daode possesses a similar ability known as Seer's Vision, enabling him to predict a person's future actions, concealed abilities, future abilities, and even the most likely trajectory of their life based on information collected on them. Daode typically has 99.9% of accuracy. But with Huan Yi, he struggles to exceed 70% and find out concrete details, even with Shiyuan's help.
-Heaven and Earth Shift: A straightforward Karmic Power developed by Huan Yi in ancient times and sealed in the Manuscript of Forbidden Secrets. Enables him to exchange injuries with his opponent, then return the two to their original positions before the start of the battle.
-Body of Great Rage: An ability stolen from one of the 11 elder Regents. Condenses a monstrous red and gold flame apparition that multiplies the user's physical abilities while casting a formless domain that increases the ambient temperature beyond solar levels. Huan Yi likes combining this ability with the Evil Eye of Tyranny to trap his enemies in a living hell.
-Thousand Incarnations of the Supreme One: Stolen from the First Regent. The most broken of all avatar/incarnation abilities. This ability summons 1,000 perfect avatars, each with 100% of the user's battle prowess and abilities. The avatars can be maintained indefinitely, but can also fuse with the user to multiply their battle prowess by e^1,000 for a couple minutes.
This basically means that for a couple minutes, the average Higher Realm warrior can become the most powerful entity of the Three Realms.
Because of this ability and other factors, Huan Yi suspects that the First Regent is at the very least as powerful as he was in his previous life—probably much stronger. It is also undeniable that, if not for its shackles, the First Regent could destroy the Three Realms in the blink of an eye.
Note that Yuanqi and the First Regent of Hell are the only creatures that Huan Yi recognizes as being able to threaten him in an actual fight.
-Shrill Cry of the Demon Child: The most powerful of Huan Yi's offensive mantras, and the spell that gave him the name "Demon Child." After uttering an ear-splitting dragon roar, Huan Yi's voice starts regressing, going from adult to teen, from teen to child, and from child to infant. Here, the cries of his dead daughter start echoing as well, fusing with his regressed voice to ripple as far as Huan Yi allows them to spread.
Anyone that fails to stay stoic under this cry will have their sanity, life and death controlled by Huan Yi. But without colossal reserves of Spiritual Energy and extreme mental fortitude, even the most heartless of men cannot resist it.
Note that this ability conceals the Power of Chaos, among other things, making it extremely difficult to control.
-Wailing Infant Tribulation Mantra: A weaker and more manageable version of the previous mantra. Forces the targets to confront a tribulation of black lightning for every infant that died a wrongful death since the dawn of time. While the black lightning attacks the body, the pain and voices of the infants directly attack the soul, often causing insanity before death.
-Law Rejecting Mark: A crimson ouroboros mark imprinted on the bearer's soul. This mark gives its bearer the ability to ignore the Power of Rules. One has to be born with the Law Rejecting Mark. And there is currently no way to share it. At the moment, only Huan Yi and Xingtian are known to possess Law Rejecting Marks.
-Twin Sacrifice of the Wailing Thearchs: A forbidden mantra cast by Huan Yi on Ailong and himself. We don't know what it does yet, but following its use, Ailong vanished, and Hundun remarks that Huan Yi now gives the impression that he no longer belongs to this plane of existence.