- "Alec cuts off all physical senses—sight, touch, hearing, etc.—from anyone, human or vampire. He is also able to extend his power over a large group of humans or vampires at the same time. His gift manifests as a mist, nearly invisible, that moves slowly away from himself toward his object, blanketing all the space in between. He is able to project this mist several hundred meters. He can also control who his mist affects, allowing the other Volturi soldiers to kill his senseless victims easily."
- ―Entry on Alec's gift[src]
Alec can use this power on more than one person at the same time, and it takes the form of a slow white mist—like fog—that gradually moves toward its victims. It is the opposite power of Jane's gift but is equally powerful and much more effective in battle. The Volturi would use it to paralyze their victims' sense of feel if they felt kind towards them, so that they wouldn't feel the pain of being killed. It can be used like an anesthetic, but this doesn't happen often. The only example given is: If there are witnesses to an unforgivable crime, Aro may feel kind to them, as they have done no wrong; they have only witnessed and not committed the actual crime but they still need to be destroyed nonetheless.
When his power touches Bella's shield, she says that she can "taste" the power and that it has a dense, sweet, cloying flavor that dimly reminds her of the numbness of Novocain on the tongue.
The mist he creates moves accordingly to his will, allowing him to select individuals he wishes to target while leaving others alone; this allows the other guard members to easily execute their enemies. He can also manipulate the effects into merely incapacitating few senses, or incapacitate them all at once, as described in Breaking Dawn when Edward and Bella discuss his power.
In the movie, he channels the power through his hands; it takes the form of a visible black smoke that slowly moves toward his target, though he can retract it with his mind.
It is one of the few mental abilities that actually has a physical manifestation, in Alec's case it is a black mist. In the movie, Alec is clearly described as being more powerful than Jane, as Alice says with regard to the twins "Alec is even worse".
Although this gift is powerful and affects several targets at once, it takes a few seconds to take effect on the victim as the mist flows toward him. During this time, the enemy can either attempt to escape or attack the user before his power takes effect, such as when Toshiro outran him, and when Emmett attacked him respectively (movie only). It also only lasts for as long as he is able to focus, and on whoever is in his sight. For this reason, Alec is often protected by the Volturi guard, allowing him to use his power without interruption.
In Breaking Dawn, Alec attempts to cut off the Cullens' senses and those of their allies while the leaders talk about the punishment to be given, but with Bella's shield, his ability is deemed useless.
Alec's power manifested already in human form, though it was much weaker and unstable. Whenever someone treated him and his sister with kindness, they were always rewarded with fortune, and those who did the opposite always met misfortune. Eventually, the villagers became too frightened with him and his sister that they decided to burn them at the stake. While being burned alive, Alec focused all of his power into escaping the pain that was tearing him apart, which sharpened his power into a specific form right before Aro saved them and changed them into vampires.
The traumatizing experience allowed Alec to utilize his power into cutting off people's senses.
A decade after their transformation, Alec and Jane displayed their powers in battle for the first time to eradicate the Romanian coven's army of over 100 recruits. With these powers, they easily destroyed the entire army and their names were spread throughout the world. Whenever a large coven was involved in a crime, Alec would be ordered to cut off the members' senses and let his teammates kill them off. Since his power could affect an entire Group at the same time, no one has been able to escape unless he let them.
- "… He cuts off your senses altogether. No pain, but also no sight or sound or smell. Total sensory deprivation. You are utterly alone in the blackness. You don't even feel the pain when they burn you."
- ―Edward's description of Alec's paralyzing power.[src]
Alec attempts to use his power to cut off the senses of the Cullens and their allies. Benjamin attempts to halt it with his power, but fails due to Alec's gift being mental while his is physical. However, Bella's psychic block renders his power useless. The mist swirls around her shield and shows the size of it, and doesn't relent until Aro tells the Volturi to leave in peace.
In the movie adaptation, he uses his power to immobilize a Japanese nomadic vampire named Toshiro to allow his masters to interrogate him about his allegiance to the Cullens. He tries to inflict Bella's shield with this power after Jane's failed, but Aro interrupts him before he can reach far, presumably knowing that he wouldn't be able get past Bella's blockage.
- Jane—Alec's twin sister—has the exact opposite of his gift. She can make any one person she focuses on experience excruciating illusory pain of fire, which is comparable to the pain of being burned alive. Like Alec, her power is merely a powerful illusion.
- Zafrina has the gift of illusion: she can make others see what she wants them to see. Her power is also long ranged, and works instantly. This power is similar to sense deprivation in the way that it can block the sense of sight, making the target see nothing at all. The illusions she projects are so real that someone can easily be fooled.