Sergei was said to be an expert in magic and often aided the British Men of Letters, when they were met with an unsolvable problem. He had been contacted by Arthur Ketch several times, even though he never met him in person. During The Apocalypse, he met Gabriel and helped him with a cloaking spell, obtaining some of Gabriel's grace as payment.
In Unhuman Nature, Castiel found Sergei through Arthur Ketch. As Castiel approached Sergei, he trapped him in holy fire. After learning that Castiel was alone, he released him. Sergei assured Castiel that his job is solving the unsolvable and gave him a spell and a vial of Gabriel's grace. As payment, he asked Castiel to tell Sam and Dean that they owe him one.
As Sergei's spell didn't work and made Jack's condition even worse, Castiel called him for help. The Shaman told Castiel it was just an experiment. Castiel threatened Sergei, that if Jack dies, he would find him. An unfazed Sergei responded with "you can try".
In Last Call, Castiel calls Sergei for help, surprising him as Sergei didn't expect to ever do business again with Castiel after the last time. Castiel reluctantly asks for Sergei's help with healing Sam's wound which Castiel can't do himself as it is divine; Castiel states that he believes that Sergei owes him after what happened with Jack. Sergei claims that he would help, but he is spending the weekend with his niece. Annoyed, Castiel threatens to find and burn Sergei alive if he doesn't help him that night. Sergei worriedly notes that Castiel's negotiation technique has improved before Castiel hangs up on him.
Sergei later arrives at the Men of Letters bunker where he determines that Sam's wound goes all the way to his soul and he is dying for Castiel's probing has caused Sam's soul to stretch, with the result being that it will eventually snap if stretched too far for too long. Sergei pretends to heal Sam, but only makes the wound worse and demands that Castiel and Eileen Leahy find the Key to Death for him in exchange for Sergei fixing Sam. However, Castiel reveals he has leverage and tells Sergei that he had Bobby Singer watch Sergei's niece, threatening to harm her if Sergei doesn't fix Sam. Beaten, Sergei restores Sam to consciousness and, though the wound remains, he is no longer dying. Sergei questions if he and Castiel are good; Castiel answers they are "for now." Sergei is impressed how "very Russian" the new Castiel's negotiation technique is before leaving.
Powers and Abilities
Sergei is incredibly powerful, since even the British Men of Letters gave high respect to him and his reputation is said to be "stellar".
- Shamanism - As a shaman, Sergei can "realign the harmonics of the universe" and is skilled in art of magic. He is called a professional by the British Men of Letters who often sought him out. His talent was even recognized by the Archangel Gabriel, who used one of Sergei's cloaking spells to hide out from his siblings.
- Supernatural Knowledge - Sergei is an expert in mysticism, esoteric and divinity and possesses a vast knowledge, even that lacks to another high specialists, as brothers Winchester, Castiel or Rowena MacLeod. He knew a procedure to slow a nephilim process of decaying, something that not even hunters and witches did, and he also states the he's been crossing the world studying and observing the skills of myriad witches, seers, holy men and others.
- Spell Casting - He has extraordinary knowledge of spellcraft, like a recharging spell, cloaking spell, holy fire and it is implicit that he can hide himself from anything.
- Supernatural Concealment - He invented a spell that succeeded to hide Gabriel from his brothers. He also sounded completely sure that Castiel, a seraph, would be unable to find him.
- Healing - As a shaman he claimed to be first and foremost a healer.