Supporting
Kim Jung-nan as Taluipa
Younger sister of King Yeomra (supreme ruler of the underworld), and wife of Hyunuiong. She works at the Afterlife Immigration Office managing the list of dead souls and gives missions to Lee Yeon. She appears to be cold-hearted but has a strict motherly affection for Yeon who calls her "Granny" in return. She had a son named Bok-gil who cannot undergo reincarnation because he committed suicide by jumping into the Samdo River, as a result of her decision to kill his beloved woman infected with the plague.
Ahn Gil-kang as Hyunuiong
The gatekeeper of Samdo River, the husband of Taluipa and father of Bok-gil. He also works at the Afterlife Immigration Office and briefs dead souls before entering the underworld. He appears to be both obedient and scared of his wife, who "wooed" him in debased parodies of the folktale Fairy and the Woodcutter and the Korean drama I'm Sorry, I Love You, before committing bossam (forcefully marrying him).
Hwang Hee as Goo Shin-joo
Lee Yeon's loyal subject and friend, also a gumiho. After having bewitched innocent humans to lose their minds in revenge for his sisters who were killed by human traps, he fled from the former mountain spirit he served to save his life and ended up at Lee Yeon's forest. He was saved by Lee Yeon, who refused to return him to the mountain spirit and since then decided to dedicate his life for him. In present day, he is a veterinarian who can speak to animals using his magic necklace. He liked Ki Yu-ri from the first time he met her, when she stole his necklace.
Kim Soo-jin as Snail Bride / Bok Hye-ja
Owner of the "Snail Bride", a traditional Korean cuisine restaurant where Lee Yeon and Nam Ji-ah's team at TVC Station usually dines in. She's a widow living for hundreds of years already, and is knowledgeable about all the supernatural beings in the world. Her husband was devoured by a tiger through the Spirit of Darkness's trick on someone's greatest fear.
Kim Yong-ji as Ki Yu-ri
Lee Rang's loyal accomplice, a young gumiho from Russia. Five years prior to the current events she was saved by Rang from a zoo where she was being maltreated. As her way of payment for saving her life, she eagerly carries out Rang's orders in causing trouble to his enemies. She assumed the identity of the 24-year-old director of Moze Department Store who died while trekking in Nepal.
Lee Tae-ri as adult Imoogi / Lee Ryong / Terry
Kim Tae-yul as young Imoogi
A serpent beast in human form, the nemesis of Lee Yeon, who has the power to read others' minds. He was born in Silla as the 9th son of a Jingol family, but with physical deformities similar to a snake. His father considered him a monster that needed to be got rid off, and on the advice of a midwife who stopped him for fear the child might be cursed, on a certain day of a leap month of a leap year, he was sealed up in a cave used to dispose of plague victims, who promptly devoured the child and transformed him into a white serpent. To escape his dark prison, (similar to Korean folklore) he waited beneath the waters for 1,000 years to become a dragon but was disqualified after a human spotted him as he was about to ascend, turning him into an Imoogi. The first person to treat the Imoogi with kindness was Taluipa & Hyunuiong's son Bok-gil, but not wanting to see his happiness, infected Bok-gil's lover with the plague, causing him to lose his mind and commit suicide at Samdo River. To satisfy his ambition of becoming a mountain spirit, he then possesses the body of the King of Joseon, Ah-eum's father, as host. To save her father, Ah-eum allowed the Imoogi to possess her body for him to meet Yeon, who killed him while inside of Ah-eum. Centuries later he eventually washed up at Eohwa Island in 1959 during Typhoon Sarah as an "impure thing" and was thrown into a covered well. To be resurrected, the island's shaman lured young women as human sacrifice every 15th day of the 7th lunar month; and despite the failed sacrifice of Ji-ah, was eventually reborn (with the help of Kwon Hae-ryong and Lee Rang) through her spilled blood, all but one of the residents of Eohwa Island, and inadvertently Lee Yeon's powers. As a child, the Imoogi sucks his babysitters' life force (turning them into mummified corpses) as his meal to be fully grown in a short period of time, and as an adult assumes the physical appearance of Bok-gil. His new goal now is to possess the body of Lee Yeon and be the new mountain spirit of Baekdudaegan, with Nam Ji-ah as his bride. With the help of his servant, the CEO at TVC Station, he disguised himself as Terry, an intern in Ji-ah's team at TVC Station. Similar to Korean folklore his weakness is horse blood, and the method of his resurrection is the same method to fully vanquish him.
Jung Si-yul as Kim Soo-oh
A young boy who is adopted by Lee Rang. In his previous life, he was Geomdung, the black puppy raised by Lee Rang which was given to him by his brother Lee Yeon, and he died due to a fire set by humans in the mountains 600 years ago. Soo-oh first appeared as a kid at the park met by Lee Yeon. Later on, Soo-oh immediately recognized Lee Rang at the sidewalk, though Lee Rang initially does not reciprocate. Soo-oh found the Eyebrows of the Tiger in the form of glasses which can make its wearer see the past life of another. Rang retrieved it from him and upon wearing, discovered Soo-oh is indeed the reincarnation of his beloved Geomdung. Later on, he was saved by Rang from his abusive step-father.
Um Hyo-sup as Kwon Hae-ryong
The CEO of TVC Station, who is secretly the Imoogi's mysterious servant. He served during the reign of Ah-eum's father. As he sacrificed his wife and children to the Imoogi in exchange for extending his life, he is described as a living corpse, since he prolonged his life for centuries by consuming human spirits trapped in bladder cherries (in Korean folklore lured snakes). He also saved Lee Rang's life after he was supposedly killed by Yeon, thereby making Rang indebted to him. He, as a man in a navy blue suit with the criminal branding "Seogyeong" ("Western Capital", which was Pyongyang during the Goryeo period; the punishment rendered towards surviving rebels involved in Myocheong's Rebellion, whose headquarters were located at said area) on his forehead, caused the car accident of Nam Ji-ah's parents. He eventually betrays the Imoogi, and is in turn killed by him while possessing Ji-ah's body.
Jung Yi-seo as Kim Sae-rom
A writer at TVC Station and Ji-ah's teammate. In her past life, she was Ah-eum's handmaiden during her exile, and she was killed by her mistress while possessed by the Imoogi.
Kim Kang-min as Pyo Jae-hwan
A PD assistant at TVC Station and Ji-ah's teammate. In his past life, he was Ah-eum's personal eunuch during her exile, and he was killed by his mistress while possessed by the Imoogi.
Joo Suk-tae as Choi Tae-suk
Team leader of Nam Ji-ah, Kim Sae-rom and Pyo Jae-hwan, who woos Bok Hye-ja. He is revealed to be the reincarnation of Bok Hye-ja's deceased husband.
Kim Hee-jung as Lee Young-sun
Nam Ji-ah's mother who is a doctor. She went missing since the Yeou Gogae accident 20 years ago and revealed to be turned into a bladder cherry along with her husband. She and her husband were eventually released from her otherworldly prison through Lee Yeon & Lee Rang's help.
Song Young-kyu as Nam Jong-soo
Nam Ji-ah's father who is a professor. He went missing since the Yeou Gogae accident 20 years ago and revealed to be turned into a bladder cherry along with his wife. He and his wife were eventually released from her otherworldly prison through Lee Yeon & Lee Rang's help.
Shim So-young as the Spirit of Darkness, the Imoogi's partner who preys on someone's greatest fear. She appears as a lady peddler in a green outfit, targeting her victims by giving away bottled juice for free, then showing them a door that will open towards their greatest fear with the victims hearing the "Doorkeeper Game" from Ganggangsullae, and as they engross themselves with their own fears they slowly die. She has been part of Korean urban legends but rarely anyone could even recall her name in the present day (which turns out to be her own greatest fear: the fear of being forgotten). Among her victims were Bok Hye-ja's husband and through the Imoogi's bidding, Lee Rang, Nam Ji-ah & Lee Yeon as well. Ultimately, she was killed by Yeon after he tricked her to enter his subconscious and taunted her with her greatest fear (Ep. 8 & 9).
Woo Hyun as the Jangseung of Yeou Gogae who appears as a mysterious old one-eyed drunkard. He first appeared at a bus stop where Nam Ji-ah was supposed to board a bus that went into a fatal accident later. He annoyingly grabbed Ji-ah's leg to stop her from boarding which also meant saving her life. She volunteered to carry him on her back going home but asked to be dropped off by the side of the road. Later on, he involuntarily gave Rang the lead to obtaining the Eyebrows of the Tiger (Ep. 1 & 5).
Son Woo-hyeon as Jung Hyun-woo, a security staff at TVC station whose true form is a Bulgasari (Ep. 2, 9 & 16).
Lee Kyu-hyung as Governor / Moon Bear, a former mountain spirit and best friend of Lee Yeon (Ep. 6 & 15). He currently resides at a Korean folk village with other supernatural spirits under his care playing their parts entertaining tourists. He owned the Mirror of the Moon, one of the four gems of the four mountain spirits. He provided a crucial lead on the disappearance of Nam Ji-ah's parents, revealing that Ji-ah was in fact the actual target in the first place.
Lim Ki-hong as King Odo Jeollyun, the 10th and last Afterlife judge who is in charge of the Darkness Hell as well as of reincarnation. He would occasionally leave his post to stay in the human world. He is first seen as a mysterious fortune teller with white eyes, who trades powerful objects with the most precious thing in someone's life. Through him, Lee Rang traded his brother Lee Yeon in exchange for the Eyebrows of the Tiger. In turn, Nam Ji-ah traded her fox bead to redeem Lee Yeon (Ep. 6 & 16).
Lee Jung-min as the bride whose true form is a gumiho. On her wedding day, Lee Yeon pursued her to execute the punishment by death for the crimes she committed against humanity (Ep. 1).
Kim Young-sun as a shaman who attempted to sacrifice Nam Ji-ah to the Imoogi. She was the one who discovered the Imoogi when he was swept into Eohwa Island and was hidden inside a covered well for safekeeping. She then distributed shamanist folk paintings of the Imoogi disguised as the Dragon King towards the island's fishing community, while also luring young women into the island to be sacrificed for Imoogi's resurrection. In return for her loyalty, she was bestowed long life and youth, until Lee Yeon killed her while rescuing Ji-ah from being sacrificed to the Imoogi (Ep. 2–3).
Do Yun-jin as Seo Pyung-hee, daughter of Seo Ki-chang. She is the only one who did not mysteriously disappear on the island; however, she is the one who cursed her father's crew-mates with the help of the shaman & Lee Rang (Ep. 2–4).
Maeng Bong-hak as Seo Ki-chang, father of Seo Pyung-hee, who was murdered and eaten by his crewmates when they were lost at the sea (Ep. 2–3).
Ji Heon-il as Jin-sik, a fisherman (Ep. 2–3).
Jang Yong-chul as a fisherman (Ep. 2–3).
Keum Dong-hyun as a fisherman (Ep. 2–3).
Kim Gui-seon as fishing boat captain (Ep. 2–3).
Kim Sun-yool as a mountain spirit bound to a tree. She relayed what scant information she knew about the Imoogi, and was later released by Ji-ah (Ep. 2–3).
Joo Boo-jin as an elderly woman (Ep. 2–3).
Park Seung-tae as an elderly woman (Ep. 2–3).
