Illusions

Illusions is the ability of vampires, hybrids, witches and immortals to project extremely realistic illusions into the minds of others by altering the perceptions of reality conceived from sensory distortions be it accidental or forcible.

Illusions, like the ability dream manipulation, exists as a subsection of telepathy.

Illusion casting
Witches have shown different versions of the ability, from implanting images in peoples' minds, to creating a seemingly infinite graveyard.

Immortals
Immortals have been shown to do a variety of things with their powers of illusions.
 * 1) Stimuli manipulations: Silas is able to cast strong realistic illusions that can plague the various senses of his victims. His illusions are a combination of visual, auditory and tactile. (Immortals are able of both physical and non physical shapeshifting)
 * 2) Shapeshifting: There is no physical shapeshifting involved. Silas merely gets into people's heads and makes them believe they're seeing someone in front of them. He can do this while being physically away from the victim and can use it to his advantage by casting illusions of speedy movements, enough to baffle vampires. In some cases he is physically present and hides himself from view using illusions.
 * 3) Voice mimicking: Silas uses his powers of illusion for voice mimicking the person he has into for further convincing his victims.
 * 4) Complete visual manipulations: Silas can cast illusions of natural phenomena like wind. He did this when he wanted to convince Bonnie to help him while in the guise of Shane.
 * 5) Tactile simulation: Silas' illusions have a tactile feeling which further convinces his victims what they see is real.
 * 6) Other sense manipulations: Silas can manipulate various internal senses like the sense of pain and suffocation. He was able to make Klaus writhe in pain after making him believe he was staked. He made Caroline believe she was dead. He made Bonnie believe that the air had thinned around her.

Vampires
There are quite a few instances where it can be seen that vampires too possess a far lower degree of the ability to cast illusions. For most vampires this ability is present in the form of dream manipulations. Damon and Katherine have been able to cast dreams into unsuspecting victims.

Elijah and Klaus have both shown the ability to project images into the minds of others.

Witches
Witches have the ability to cast illusions as well via spells ranging from simple to the complex.

Trivia

 * For vampires, it is an extension of their tactile Telepathy, allowing them to enter minds similar to their ability of Dream Manipulation. However, this is done on a victim which is conscious.
 * Their ability to enters other mind is dependent on whether said mind is weaker or willing, older vampires use this skill more effectively, implying that mental strength too, like their physical strength and speed, also grows and evolves with age.