Castiel manifests on Earth through possession of a vessel – in his case Jimmy Novak. On one occasion, Castiel describes his true angelic form as a “multidimensional wavelength of celestial intent” ; on another, he says that his true form is the size of the Chrysler Building in New York, which is 1047 feet (319 m) in height.
The sight of Castiel’s true form will burn out a human’s eyes, as Pamela Barnes found when she tried to summon him in a séance Castiel’s true voice, like the true voices of other angels, is piercing to the human ear. He communicates with his vessel Jimmy through the electronics in his home, and appears to use an analogous method to communicate with Dean and Sam in Heaven Castiel can also speak to his vessel unaided; he converses with Jimmy to obtain his consent to serve as a vessel Castiel, using his vessel, can easily overpower and kill demons, sometimes even groups of them, by touch.
Castiel is able to teleport himself, and in some cases groups of people, through time and space. He can cover great distances in a matter of seconds, as shown in 6.06 You Can’t Handle the Truth when he believes Gabriel’s Horn of Truth has been discovered, and searches an entire city in moments. The angel possesses vast occult knowledge, ranging from lore, to spells cast in Enochian, to the structure and defenses of Hell. Cas can move objects with a gesture. Castiel is also proficient with an angel blade, generally outmatching his angelic opponents while using it.
Castiel rank in the Host of Heaven has varied, and the abilities he displays have varied based on his changing status. Castiel states that he was once the captain of his garrison. In the past Anna Milton, in her angelic state, was his superior in their angel garrison. Uriel appears to be junior to him, until he is promoted when Castiel’s superiors become concerned about Cas’ empathy for Dean. Zachariah was also his superior. However, Castiel seems to have been higher in rank than the henchmen that often accompanied Zachariah. Castiel indicated that he had been cut off from Heaven after helping Dean escape from Zachariah, meaning that he lost some of his abilities, including the power to heal. After banishing himself and a group of other angels, Castiel loses more of his powers and appears almost mortal at the end of season five. Castiel states on one occasion that he is now a Seraph and as a result, seems to hold onto all of his powers even though he is a fallen angel and cut off from Heaven again. However, since returning from Purgatory, his powers are weakened, leaving him exhausted when he uses his major abilities. However, this seemed to be a temporary effect as he has since shown his powers with no ill effect.
Castiel has been killed four times, once by Raphael, once by Lucifer, once by the Leviathans,and once by a reaper who was hired by Bartholomew. He is subsequently resurrected each time. After he died and returned the second time Castiel stated that he believes God brought him back “new and improved,” by the third time he began to see his resurrections as punishments for all he’s done. He is able to heal others with a touch and resurrect people at will., He demonstrates pyrokinesis when he burns “Crowley’s” bones. Later, Castiel shows the ability to incinerate lesser monsters, such as the vampire Lenore, by touch. He also releases a blast of white light from his palms that instantly kills anything that sees it. It is also implied that he can kill even powerful demons with ease, including Crowley, the King of Hell, he is even able to force one back into its meatsuit to kill it. Despite his improved abilities Castiel remains unequal to an archangel, as Raphael can block his attempt to kill Crowley, as can Eve and the Leviathans.
He also displays the unique ability to tell the Leviathans apart no matter what form they take. According to Meg this is due to the Leviathans briefly using him as a vessel, which allows him to know them “better than anyone.” He also displays the ability to sense the presence of nearby Leviathans before they become known to anyone else.
Source – Super-Wiki