Antimatter Tentacles

The Antimatter Tentacles, or simply Tentacles, are the product of Yanagisawa's antimatter research and the material Korosensei is composed of.

The tentacles are a major plot device used in many significant events, such as Korosensei's creation, Itona Horibe's character arc and the revenge of Akari Yukimura.

Overview
The tentacles are the by-product of Yanagisawa's attempt to produce antimatter within the human body. Although flexible and soft, the tentacles can possess very high levels of strength and speed when weaponized. All Tentacle-based lifeforms are vulnerable to Anti-Sensei Weapons; the unique cellular tissue of the tentacles will disintegrate upon contact with said weapons.

According to most individuals who have been implanted or augmented with the tentacles, the latter will ask them what they wish to be and will act (in a way) accordingly. Notable examples of this occurrence include the following:
 * Korosensei requested to be weak, which prompted the tentacles to riddle him with numerous weaknesses as well as give him his current appearance.
 * Itona Horibe desired strength, so the tentacles forced him to focus on fighting and winning.
 * Akari Yukimura wished to become an assassin who blended in until the ideal opportunity presented itself. In response, the tentacles concealed themselves within her neck until her first attempt to assassinate Korosensei.
 * Reaper wished to be noticed by Korosensei and was made stronger and more powerful than him.

Notable Physiology
Color Changing: A tentacle-lifeform can change their skin to any color and/or pattern. This attribute can be utilized to convey messages, expressing emotions, as well as for disguise and camouflage.

Regeneration: If one or more of a tentacle-based lifeforms tentacles are maimed, they can regenerate the severed limb. Afterwards however, this temporarily weakens their stamina and their reaction speed is temporarily reduced.

Molting: A once-a-month occurrence, a tentacle-based lifeform can shed their skin. In addition to being an excellent decoy and escape method, the skin can be used as a protective membrane, either for themselves or another individual, protecting them from being hurt, even from military-grade explosives. Afterwards however, this temporarily weakens their stamina and their reaction speed is temporarily reduced.

Shapeshifting: The tentacles can be made to change shape. One such example is that they can be transformed into drills or into a large spider web.

Poison Immunity: Tentacle lifeforms are immune to toxic substances that would definitely kill an ordinary human. Although, such substances do affect then, such as by transforming their head.

Mucus: An antimatter organism can produce a thick mucus from anywhere across their body. It has varied uses and support applications; such as being viscous enough to stop a bullet, and it can make water congeal into gel.

Water Absorption: Upon contact with water, a tentacle will absorb it like a sponge and swell up, and thus its mobility will be hindered. This can be partially negated if mucus is used to turn it into a gel; if the tentacle's mucus were to be depleted, this protection is unavailable.

Energy laser: Tentacle-lifeforms are able to discharge a large beam of energy, as shown with Korosensei and the transformed Reaper.

Superhuman senses: Korosensei has highly acute senses and can detect even the most minuscule changes and abnormalities in the surrounding temperature, light, sound, and smell. Despite having no visible ears or nose, Korosensei has proven to be able to hear things no normal human can pick up on, as well as detect the most minor of aromas, which aided him greatly in evading the assassination attempts of Class 3-E. Korosensei is especially talented in identifying people by their smell, as well as certain materials (such as explosives and poisons). His eyes are also quite keen, and can keep track of objects going thousands of miles per hour without difficulty, as well as detect the slightest of movements that occur quicker than the blink of an eye.

Superhuman digestion: Korosensei can digest anything, aside from Anti-Sensei weapons, as his teeth can crush any hard materials. Whether he eats something or it enters his body, he can either melt the food first then eject it, or it will just be digested. Although it is not guaranteed that Korosensei will receive no irregularities from what he has eaten, it usually has no tactical disadvantages if it is not a weakness for him.

Potential Enhancements
Liquefaction: After drinking a certain chemical formula, a tentacle-being will gain the ability to control their fluidity, allowing them to morph into a mass of mercury-like slime. At the cost of their anthropomorphic-type body and tentacles, the tentacle-lifeform can fit through any space while retaining their full speed and most of their abilities.

Quality over Quantity: A tentacle-based life form can utilize a reduced number of tentacles. By doing so, the remaining tentacles become stronger and faster.

Tentacle Creatures

 * Main articles: Korosensei § Powers and Abilities, The Reaper § Powers and Abilities

The first instance of the tentacles. These life forms possess numerous powers and abilities, such as being able to regenerate upon damage and tremendous speed and strength.

However, tentacle creatures carry a risk of explosion once its cells reach the end of their division cycle. This depended on the size of the organism; the smaller it is, the higher the risk of explosion. For Korosensei, as he is both quite large and the progenitor for other tentacle creatures, his risk of explosion was less than one percent at best. It is even possible to remove this risk entirely, as shown with Reaper II's tentacled form.

Human Body Tentacle Weapon
A human can wield the power of the tentacles by injecting the tentacle seed into their bodies. Upon being implanted, the tentacles will bond themselves to the user's neurons and a varying number of them will sprout from the place of injection. Once this short process is complete, the tentacles will act on the will of the host.

In turn, the user will experience a multitude of harmful side effects and symptoms. As the tentacles and the human body have vast genetic differences, the most common symptom is excruciating pain. As stated by Itona and Kayano, the tentacles will absorb most of the host's energy through their neurons and as a result, will significantly hinder their natural abilities.

Without regular maintenance, the tentacles will quickly eat away at the user's mental stability and life force until the user dies. This occurrence can be identified through their eye color; the user's irises will turn black with yellow pupils and their scleroses will turn red. A notable example of this phenomenon is when Kayano had endured the pain of the tentacles for nearly the entire year without any upkeep, and became deranged in a few dozen seconds upon using her tentacles to their full extent.

Side Effects
Yanagisawa's research team compiled a full list of side effects for this variant of the tentacles: "#Acute Pain: Combining the human body and a genetically different life-form causes extreme organ rejection. The transplant recipient will experience pain on a daily basis. It requires a massive amount of energy to stabilize the recipient and prevent rejection.
 * 1) Decline in Performance: The bonding with the recipients neurons initiates a decline in the precision of neurotransmissions, resulting in a 10% to 30% decline in mental and physical performance. Therefore, the recipient must either receive further body modification or use their tentacles to compensate for the decline in physical performance if they are to be used for battles on warfare.
 * 2) Mental Instability: Because the tentacles are linked directly to the recipient's neurons, in some cases, excess tentacle energy will overstimulate the brain. This overstimulation can trigger bouts of rage which can physically damage the recipient and are extremely dangerous to both the recipient and others.
 * 3) Metabolic Instability: The recipient's body temperature is frequently observed to rise while the recipient simultaneously experiences a chill in the thoracic region. This is probably attributable to the fact that the organ, which is equivalent to the heart of the Perfect Tentacle Creature, did not originate inside the body of the transplant recipient. The chill is merely a sensory abnormality, but the rise in temperature may have negative ramifications for the body and mind of the recipient if it continues for a long time.
 * 4) Aversion to Water: Due to osmotic pressure, the movement of the tentacle is dulled when it comes in contact with water; thus recipients tend to instinctively avoid it. However, water merely destabilizes the balance of the tentacles, and no serious repercussions are currently known to occur.
 * 5) Change in Eating Habits: There is a tendency for recipients to develop a sweet tooth. This is thought to result from the recipient requiring a large amount of energy to maintain a connection with the tentacles; however, no serious repercussions are currently known to occur from this condition either.
 * 6) Major Obsession with Certain Body Parts: The recipient will develop a strong obsession with soft-tissue parts of the human body. It is presumed that the tentacle feels a strong sense of fellowship with these body parts because of their similar consistency. However, this preoccupation could be linked to number 3, so some caution is recommended in this regard."

- Documents from Yanagisawa's organization

Yanagisawa's Variant
During the climax of the series, Yanagisawa revealed that he had created a modified variant of the tentacle seed to grant him the powers of a tentacle creature while still keeping his human qualities, which worked by strategically implanting tentacles into his vital organs.

Yanagisawa possesses none of the side effects of the conventional tentacle seed, but in turn his body is vulnerable to any variant of an anti-sensei weapon.

Tentacle Mines
This form of tentacle weaponry worked by placing a live tentacle inside a container equipped with a sensor, which propelled itself at supersonic speed at a detected life form. These were not effective against tentacle creatures, but proved otherwise against humans; as shown with Aguri Yukimura.