I wanted to reply earlier but I wanted to finish part 2 first! I just finished today so here’s what I have to say:
I agree with you, Park Yeonjin was an incredibly well-written villain and her portrayal by Im Jiyeon was simply brilliant. In my opinion, her character stole the show; from her psychotic behaviours to the way she carries herself, her mannerisms and way of talking, she was mesmerizing and downright scary. I really want to applaud Im Jiyeon, I think she’s mainly what made Park Yeonjin such a interesting character. I am definitely going to remember her as one of the best kdrama villains! (Also big props to Shin Yeeun, she also did a terrific job in her portrayal of young Park Yeonjin.)
I don’t have much to say about the other antagonists tbh. They all got what they deserved. Jaejun’s fate was especially satisfying.