By drinking this dark essence pulsing with an enormous amount of power, you become a being capable of killing that which cannot be killed.
*Your mind, body and soul are elevated to the point that your body is strong enough to beat the Skyfathers to a pulp and take their blows without a single scratch on your nigh-indestructible body. Your mind surpasses the Ultimate Gods of Intelligence and Wisdom such that even a Matrioshka Brain would look like a dumb primitive monkey to your mental prowess. Your speed, agility, dexterity far surpasses the speed of light and the Gods of Travel and Speed. Your willpower is unlimited such that even if you are tortured for eternity in the flames of hell you will never break. Your soul has been made nigh-indestructible and absolutely immortal. This immortality cannot be altered or erased or otherwise affected negatively in anyway.
*You no longer need to eat, drink, produce waste, sleep or perform any other bodily needs. You may however choose to perform all of them as you see fit. You also do not age and are biologically immortal. Your mind is completely immune to things that would negatively affect it such as illusions or hallucinations or telepathy or mind control. You are also immune to memetic effects and effects like no being able to withstand looking at the true/divine form of gods and demons. Any lie detecting powers or tech or any such thing will detect what you want them to detect.
*All this perfectly culminates into a body suitable to kill the almighty gods and demons that rule the different parts of the world and the universe.
*While having a nigh-indestructible body is well and good, there will always be someone strong enough to reduce you to a pile of ashes. So this essence grants you an absurdly, enormously powerful regeneration factor that works on a Physical, Mental and Spiritual level. If your body is completely disintegrated on a quantum level you will still regenerate and come back. Your mind becomes able to heal from any damage or trauma and you remain forever mentally healthy unaffected by things like boredom or depression etc caused by your immortality. Your soul is nigh-indestructible but there will always be some goddamn over-achiever who somehow managed to specialize in destroying souls, so your healing factor is strong enough that even if your soul is erased from existence it will still regenerate and reform.
*Due to this regeneration, to truly kill you a being has to destroy you on the Physical, Mental and Spiritual level simultaneously. Only then can it be considered a true death for you. If a being only destroys your physical body but not your mind and spirit then it only counts as a physical death from which you can regenerate from. This is also similarly the case for Mental and Spiritual Deaths.
*A side effect of this absurd regeneration is that you gain a type of Adaptive Evolution that also functions eerily similar to a Zenkai Boost. First of all, this Adaptive Evolution is not going to turn you into a hideous monster like Doomsday so be at ease. The way it works is that every time you take damage from anything to your mind, body or soul all three of those aspects start building up resistances against what damaged you and you also grow in power. The more you are damaged the stronger your resistance will be and the stronger the boost that you receive in power. The higher you resistances the less damage you receive from such attacks, eventually becoming completely invulnerable. If there is any attack that would kill you in a single hit(Whether it is a Physical, Mental or Spiritual death) without even granting you an opportunity to develop your resistance then instead of a resistance you'll develop a complete immunity to that level of attack and it will take much more power to one-shot you with the same type of attack again. (For example if someone hits you with a lightning blast enough to vaporize a mountain and you take a decent amount of damage then you'll build up resistances to lightning blasts of those level. The next time you get hit with the same attack it may not leave more than a few scratches on your body. If the lightning blast completely vaporizes you and causes a physical death then you'll be immune to that level of lightning blasts).
*With the kind of intelligence and wisdom you have, it shouldn't be a surprise that your rate of learning and growth is absolutely absurd and beyond anything even the greatest gods are capable of and it only gets better to the point that your growth rate has a growth rate. This means that as you get stronger the speed at which you get stronger also increases. You have an absolutely ridiculous amount of talent for anything and everything in existence. Whether it is academics, acting, combat or anything you can imagine. You could learn and master any skills within a week and rapidly master them to beyond the most skilled of the gods in a few months at most such that you could surpass the most talented Goddess of Family at Cooking or the most skilled Smith God ever at creating artifacts/weapons etc that stand among the most breathtaking things ever created in existence or the most talented Incubus at seducing any being.
*You are capable of copying and learning and improving any magic, magic system, skill, talent, perks, abilities, bloodlines etc even if you shouldn't be capable of it. Regardless of how innate the skill is, or how rare the bloodline is you can copy it. If you have a magic that lets you copy weapons or armors etc then as a Slayer of immortals you can even copy Divine/Conceptual weapons perfectly even if it shouldn't be possible to copy them. When you copy anything, it automatically becomes at least 5 times better than the original and in time you can make all your skills not just the copied ones up to several orders of magnitude stronger and better in every way. You can remove weakness of racial traits you copy or weakness in a magic spell, everything can be improved.
*You know the perfect ways to train all your powers and improve them or remove limitations/weaknesses.
*All the above abilities are just the base abilities provided by this essence. These abilities can be further enhanced by the absolutely enormously powerful Magic Core that is connected to your very existence. This core is extremely potent such that a single drop of your magic is equal to what thousands of the greatest of mortal mages generate throughout their lifetimes and an almost limitless well of magical energy such that even the almighty Odinforce pales in comparison. This energy can be used to enhance all your physical, mental and spiritual attributes, it can enhance the power and speed of your regeneration and provides energy for all your spells. This can even enhance passive skills and bloodlines and other perks beyond what their base give you.
*Just like the Gods and Demons, you have an almost innate understanding of the life, death and the universe and all it's forces, natural, esoteric or otherwise. You can use your magic to create life, use all powerful runes to shape the universe or even create star forges to create any technology you can imagine, generate shields to stop supernovas, create Dyson Spheres and anything else you can imagine. You also gain an extremely powerful Clairvoyance that allows you to gaze into the past, present and future letting you see all the infinite possibilities and allowing you to choose which path to walk down on.
*You wouldn't be called an Anti-Immortal if you weren't capable of living up to the title. You are capable of killing anything in existence regardless of how powerful they are or how unbeatable and invulnerable and unkillable they are and Regardless of the type of immortality (Phylactery or curse of immortality etc..). Whether they be Embodiments of concepts or all powerful gods, demons or angels you can kill them. You can rip through any immunity or invulnerability any being you face has. You can use lightning to kill a God of Thunder/Sky/Lightning for example or read minds of those immune to telepathy.
*Even beings who lack the concept of death and the most bullshit forms of immortality can be killed. You can do it by applying the concept of death onto them or any other way available to you. You can also kill them without applying such concepts. You can kill those who resurrect using Time curses or loops and anything else you can imagine.
*And every time you kill anything whether mortal or immortal you become stronger. Every bit of talent, potential, physical and magical power, knowledge, skill, experience,charisma, beauty, weapons, any special abilities given by their bloodlines and everything that once belonged to your defeated foe will be yours. Such is the price of going against you. And not just that - when you kill anything they die a permanent death unless you allow their resurrection by any means
*Another ability provided by this essence is - the ability to revive your defeated/killed foe into a new species of Shadow Servants. The reason they are made of shadows is that all beings cast shadows since the day they are born. Our shadows are constantly with us every moment of our life, preserving memories and experiences. Our foes when revived as part of our shadow army don't possess the soul as it moves on to the after life after getting killed. The shadow possesses the ego, personality, the memories along with all their power. And all the powers and abilities the being had is much stronger than when they were alive. They will be completely loyal to us and incapable of betraying us no matter what whether willing or unwillingly.
*This new species will look just as they did when your foes were alive but they are made of shadows. They are capable of procreating with all living beings and each other. They essentially function as any normal species does but they are completely loyal to us. There is no limit to how many Shadow servants you can have. And any being can be revived as your servant regardless of whether they are gods or cosmic beings or embodiments of concepts.
*You have access to a separate dimension which is the 100 times the size of our solar system filled with 10 super planets which revolve around a super massive star. These planets have the best resources available in the universe. All your Shadow Servants will stay in this Shadow Dimension and eventually form a civilization better than 99.999% of the civilizations in the universe.
*Although our Shadow servants may be stronger than they were in life, they can still get hurt and can be damaged and destroyed. Now however, every time they are damaged/destroyed you can either send them back to the shadow dimension to recuperate or use your own nigh-limitless magical energy to allow them to rapidly regenerate. They can continue regenerating so long as you have magical energy available and they can never be permanently destroyed so long as you live.
*This essence does not give the option to become stronger through worship. Should you have that ability from somewhere else however then you can receive power from your servants as they worship you as their deity. And should you have the ability to be reborn into other worlds then you may take all your powers, your dimension and your servants along with you if you choose to.
*Also if you become a deity or something similar or simply through this essence, then while you will get stronger when more and more people worship you, you won't get weaker when they stop worshiping you. Also an important thing is that you won't be influenced by the thoughts/perceptions of mortals and develop split personalities or something similar. You will only change if you want to change. You also won't be bound by divine/ancient laws or something similar and can freely interact/travel with all dimensions/realms/planets etc without being weakened or losing your powers.
*If you slay gods as a god then their domains/authorities will become yours and any negative side effects of having them are nullified and these domains can be enhanced using your mana. If you're not a god then their domains will become an innate ability you can access and they function the same as before and can be enhanced with your mana. Nevertheless you'll have all the power and skill and knowledge need to use it.
*All your powers cannot be suppressed, copied, altered, nullified or affected negatively against your will. You cannot be sealed away by any magic or seals or anything similar to it.
*If you choose, you may allow somebody to seal you away and suppress your power but you will be able to escape the seal by breaking them or simply escape without even touching the seals if you don't want anyone to know you have escaped. This has the advantage of making the seals act like training wheels. The longer you have been sealed away the stronger your power becomes. Merely spending a year sealed away would double your power and it will keep doubling the longer you are sealed.
*Similarly, you may choose to sacrifice your power to defeat a great enemy and no amount of resurrection or plot armor can save your enemies from a permanent death. However, unlike other protagonists you don't lose your powers permanently if you sacrifice them to take down an enemy. Instead you will regain the power that you sacrificed after a year and when your powers return they will be at least an order of magnitude stronger.
*This sacrifice doesn't have to be all of your power as you can sacrifice a single ability to destroy an enemy. However, the stronger the enemy in comparison to you the more power you'll have to sacrifice. The strength of this sacrifice will keep increasing as you grow stronger.
*This sacrifice doesn't necessarily have to be to defeat an enemy. You can sacrifice your power to perform miracles like saving someone's life or resurrecting the dead or any other cause in which case the return of your powers will be significantly faster than if you sacrificed to destroy someone.
*You can also sacrifice certain aspects of one of your powers to enhance other aspects of your powers. For example, if you get Tiamat's Authority of Life, you can simply sacrifice your ability to create her mud/sea of life and simply keep her infinite mana/true ether and also her immense output and then enhance it even further.
*You have absolute control over all your powers and you know every possible trick and abilities your powers possess. You even retain your powers if you somehow possess another body by means of possession or crafting yourself a new body or any such method or even if you become a being of pure energy you can retain biological advantages even though it should not be possible. You can also decide if your previous bodies retain any benefit you had - leaving perks/abilities/bloodlines to the body or completely removing them rending the older bodies worthless.
*God-slaying is all well and good but it wouldn't be very impressive if you were not good at laying with others. You don't need to worry about that now, however, as your Charisma is absolutely absurd and beyond even what the most suave and charismatic sex demons can have. You could convince even the most devoted Goddess of Marriage to leave their husbands for you over the course of a night or make a Succubus consider monogamy.
*Your skills at manipulation are such that you can manipulate people incredible number of people without them being aware of what you are doing. Even the most talented Gods of Truth won't be able to tell you are doing it. You could easily start wars between entire pantheons with a few well-chosen words.
*Your skills at seduction and sex are such that you passively seduce the women around you and this yields positive results almost all the time as though you were making a casual attempt at seduction using normal methods, there are no negative consequences for failure as you are not seen as doing anything abnormal. And when you are actually trying even the most prudish and man-hating virgin goddesses can be seduced without them even being aware that you are seducing them or if you want them to be aware that can also be done. Your ability to bring pleasure is such that even the most experienced goddesses and succubus can be left into a mewling ahegao'd mess. They would devote their entire lives to you after a single romp.
*You have minor porn logic and all your fluids taste like the most heavenly substance in the entire multiverse and it creates a deep craving for more but it's not quite addiction unless they drink your blood. Any creature of night would be addicted to the taste of your blood should they experience is but once.
*You are not bound by fate, prophecy, karma and all such similar things. Your destiny is your own and no amount of curses or prophecies can decide the course of your life.
*You can adjust the power of this essence according to the world you go to if you wish.