- Angel/Devil Shipping: Dong-sik/In-woo. Dong-sik's a Nice Guy even when he thinks he's a serial killer while In-woo's a psychopath who enjoys murdering people and is obsessed with Dong-sik.
- Crosses the Line Twice: Dong-sik tries to murder Mu-seok? Not funny. Dong-sik fails terribly at murdering Mu-seok while an exasperated In-woo watches? Funny.
- Friendly Fandoms: With Strangers From Hell, another South Korean series about serial killers that aired in 2019. Some fans have jokingly suggested the shows are part of a shared universe and Seo Moon-jo and Seo In-woo are brothers (because they share a surname and are both serial killers).
- Ho Yay: In-woo is very interested in Dong-sik and says things like "I must have him". One of In-woo's "friends" even assumes Dong-sik is In-woo's lover.
- Jerkass Woobie: Ji-hoon. He's a thoroughly unpleasant person, but by the end of the series he's been kidnapped and almost murdered, held at gunpoint by his brother, seen his brother murder their father right in front of him, taken hostage by his brother (sensing a theme here?), locked up by his brother, and almost murdered again.
- Love to Hate: In-woo. Yes, he's a psychopathic serial killer who's willing to kill Dong-sik and Bo-kyung, but he's so damn entertaining to watch.
- Retroactive Recognition: Heo Sung-tae plays Chilsung. Two years later he became better-known for playing Player 101/Deok-su in Squid Game.
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