Psionic powers (a.k.a. psychic powers) are the ability of using the mind to induce paranormal phenomena. It is present to various degrees in various species.
The presence of psionic powers within a species is rare, and is dictated by their structural makeup. Even the subtlest of changes to an organism's (or species') genetic code can destroy its psionic potential. Psionic emanations can be lethal to organisms, and are not yet fully understood by terran science.
The protoss are masters of psionic powers and are natural mind-readers. The protoss can use their psionic abilities to shield themselves, charge their tools and weapons, and to make, manipulate or meld matter. A very small number of protoss called preservers have the ability to hold the memories of many other protoss from centuries or millennia ago, even claiming to hold "all the memories of the Protoss". The high templar's powers are so great that they can even focus their psionic energy to create terrible storms of psychic energy that destroy the minds of other living creatures. If two high templar would merge, they would create a creature of pure psionic energy known as an archon, so powerful that they can independently erect a resilient shield and direct psionic shockwaves.
The Khala is a structured approach to protoss psionics. It was developed near the end of the Aeon of Strife in order to restore the sanity of the protoss.
The Khala grants much control and discipline over psionic power. Being subsumed in the Khala meant a certain loss of self in addition to the gain of the "other". There was a risk the loss could be drastic. Most Judicators and Templar subsume themselves into the Khala at least once a day.
Protoss cut off from the Khala are quickly embraced by the Void. The drug Sundrop is capable of doing this, at the cost of mental imbalance.
The Dark Templar, also known as the Nerazim, cut themselves off from the Khala in order to maintain their mental independence. The Conclave believed this could create another Aeon of Strife. Lacking the control and discipline of the Khala, some powers, such as psionic storm, ran out of control.
The Void provides the Nerazim with enormously strong individual will and enabled them to learn cloaking powers very quickly.
The terrans exhibited a powerful psionic potential and are only a few steps away from developing into a formidable psionic power. Very few terrans can use psionic powers, but most that can become "ghosts". Some weaker psychics can become wranglers, used to hunt other psychics.
Terran psychics can be rated on the Psionic Index scale. A terran with a PI of 2-5 can sense psionic powers but generally cannot use other psychic abilities. Some such psychics are employed by the Ghost Program as wranglers, employed to hunt other psychics. Psychics release alpha waves which can be detected by other psychics. Other such weak psychics have demonstrated abilities such as resisting telepathy. Psychics with a PI of 5-6 are telepathic. Psychics of this level are recruited to become ghosts. Those with a PI of 8 or more have telekinesis. Ghosts generally do not have the ability to block thoughts; ghosts find each other very easy to read.
Non-psychics such as Arcturus Mengsk and Corbin Phash have demonstrated the ability to conceal their thoughts from telepaths. Phash can even think "fake" thoughts that another telepath might detect. However, the technique is not completely reliable.
Some psychics have demonstrated telekinetic powers; this requires a Psionic Index rating of at least 8. A few even demonstrate pyrokinesis (the ability to create or manipulate fire with their mind).
The zerg possess a limited degree of psionic powers, as the Overmind once established a psionic link with the xel'naga.
All zerg strains possess a degree of telepathy. However, it is different from the communication used by protoss or terrans and as such, it is normally impossible to communicate with most zerg strains. However, prior to her infestation, Sarah Kerrigan demonstrated such an ability.
The zerg are somewhat sensitive to psionics and can sense psi emitters from a great distance, even across worlds. Zerglings can sense the emanations of a powerful psychic at a considerable range.
Additionally, overlords fly using helium-filled gas sacs combined with a weak telekinetic psi-ability for lift and motive power.Changelings can alter their opponents' perceptions with psionics.
In order to gain the upper hand in the war against the protoss, whose powerful psionics were a great threat to the Swarm, the Overmind planned to assimilate the terrans, since their powerful psionic potential would make them able to fight the protoss on their own terms. To date, the only psychic terran that the zerg have been able to acquire and transform into an advanced infested terran is Sarah Kerrigan, a ghost who had been a member of the Sons of Korhal. The Overmind left her with the majority of her spirit, and she retained her intelligence and even some of her humanity. During the Second Great War, her powers increased greatly after exposing herself to the first spawning pool on Zerus.
The protoss scientific organization, PAX, conducted an experiment with creep and viruses. The resulting creature developed psychic powers, and could even "distort" the Khala (creating hallucinations) and control a unique being.
↑Yeah, I mean, basically, any protoss that is a part of the Khala is going to have an enourmous psionic energy to draw on and can create, you know, obviously, wepons and blades with it. The dark templar, you know, in all of the lore, they, because they chose to go their own way and they don’t have the power of the Khala behind them, but they have the power of enormously strong individual will. It's sort of, I’m giving a long-winded version of the answer, I think, that Chris just gave. One is pulling that power from within whereas the dark templar have to take what is around them, the void, and manifest it. It is a completely different philosophy, but both are really cool weapons. Chris Metzen, Brian Kindregan, StarCraft Legacy staff. 2010-10-23. BlizzCon 2010 StarCraft II Lore Panel. StarCraft Legacy. Accessed 2010-10-25.
↑Overmind: "Let her go, Zasz. The greatness of her spirit has been left to her; that the Swarms might benefit from her fierce example. Fear not her designs, for she is bound to me as intimately as any Cerebrate. Truly, no Zerg can stray from my will, for all that you are lies wholly within me. Kerrigan is free to do as she desires." StarCraft. Vivendi Games. Level/area: The Amerigo (in English). 1998.