Seraphim

Seraphim are a higher species of angel, above angels such as Uriel and Joshua. Zachariah is an example of a Seraph. He's worked under the command of the Archangels for at least 6 millennia.

The only known Seraphim are Castiel and Zachariah.

Their true form is very intimidating, something like thousands of feet high, with four faces, one of which is a lion, and six gigantic feathered wings.

Zachariah was shown to be extremely condescending towards demons due to his pride and superiority, and of course the fact that they detest each other by nature. Imbued with the immense power, the Seraph have such strength he could smite high-tier demons.

After God resurrected Castiel after Lucifer killed him he chose to upgrade his celestial status considerably, making him a Seraph. When Castiel regained his memories he was much more powerful than before, being able to smite several demons effortlessly. When he was a normal angel it took him a great deal of focus to kill demons with the touch, and he was not strong enough to kill demons like Alastair, which he now definitely can. It's probable that Zachariah was somewhat more powerful than his Seraph brother, since he was older.

In the hierarchy of Heaven, the Seraphim, like Zachariah, are ranked higher than Cherubim and angels, but lower than Archangels. Since Michael and Lucifer are sealed away in the cage, Castiel might be one of the highest ranking angels alive. As for now, he's trapped in Purgatory. But if he succeed in escaping, he could become the potential ruler of Heaven and by extention, of the remaining angels.

Unlike standard angels, Seraphim powers are imbued within them, meaning they still possess all of their powers, even if they become fallen angels, and are cut off from Heaven, as demonstrated by Castiel when he burned a monster to death with his mind, during his time in Purgatory unlike the first time he Fell and lost that power because he was cut off from Heaven.

Powers and Abilities
They posses all angelic powers but to an upper level than normal angels. They posses but are not limited to, as they may not demonstrated yet:
 * Biokinesis - Seraphim manipulate/influence the human body, like can inflict pain down to the molecular level, including internal bleeding, removal of lungs, and hemoragies.
 * Teleportation - Seraphim, as Angels, can move from to another, instantly; in the blink of an eye.
 * Telepathy- They can easily read the minds of humans.
 * Pyrokinesis - Seraphim can generate and manipulate fire.
 * Superhuman Stamina - Seraphim never tire, as one never gave up its search. Obviously, they do not require food, or sleep to function normally.
 * Superhuman Strength - Seraphim are extremely durable and strong. They can overpower and kill any demon and monster (except for Leviathan). They can also overpower other angels but are inferior to Archangels.
 * Invulnerability - Seraphim are immune to all convential weaponry and forms of harm, only higher beings, and special weapons can damage them.
 * Healing - They can heal others of great wounds with ease.
 * Resurrection - They can revive the dead as one of them brought Adam back to life and another brought Bobby Singer back.
 * Invisibilty - Seraphim can become invisible.
 * Immortality - Seraphim like other angels don't age or die by natural causes. However, as is the case of most celestials, they can be killed.
 * Angelic possession - Like all angels, Seraphim need a human to possess, but because it's angelic possession this needs to be with the human's consent.
 * Angelic Touch - This ability was shown by Castiel when he kills Lenore and a monster in Purgatory as well as several demons.
 * Regeneration - If their vessel is in some way injured, they can regenerate very quickly, though wounds caused by angel weapons take longer. They are immune to Earthly illness and desease.
 * Voice Mimcry - Like lower angels, Seraphim can mimic others voices.
 * Time Travel - Seraphim can travel through time, with greater ease than lower angels, they are also able to send others either forward or backwards through time, with the same ease.
 * Reality Warping - Seraphim posses low level reality warping abilities, Castiel was able to assemble a game, by shaking the box, Zachariah was able to undo all the damage Dean did to the Green Room, in a blink.
 * Perception Altering - Castiel was able to transfer Sam's madness into his own mind.

Weaknesses

 * Angel blade - As demonstrated when Dean stabs and kills Zachariah.
 * Angel-Banishing Sigil - When activated, such a mark can temporarily banish Seraphim.
 * Archangels - As angelic beings found on the highest echelon of the heavenly host, archangels can easily overpower Seraphim.
 * Leviathan - Being older than angels in general, Leviathans are able to overpower Seraphim, at least in Purgatory.
 * Common Angelic Weaknesses - They are vulnerable to Holy Oil, Heaven's weapons, etc.