Dive Into You

Moon Kyunghwa, Dami, Ryujin and Jeongyeon are pretty good close friends. But the latter three are also idols. One day, they mysteriously receive a letter in the mail that invites them and eight other male idols (Shinwon and Jinho of Pentagon, Seungkwan of Seventeen, Jaemin, Taeil and Haechan of NCT, Haknyeon of The Boyz, Seoho and Ravn of ONEUS) to a giant property in the middle of Jeju Island.
The four females and eight males team up, slowly bonding with one another. Under the light of a full blood moon, they share ghost stories, brought upon by Ju Haknyeon and Lee Seoho.
That's when the real fun begins.
Haechan transforms into a protective vampire over Taeil, Seoho and Ryujin turn into werewolves, Ravn becomes a literal raven, Seungkwan can produce flowers and has a flower crown that cannot be unattached, Jaemin possesses the ability to shoot lightning from his fingers, Haknyeon turns into a prince that rides a midnight black horse named Maverick and is obsessed with saving and wanting to be with his Princess, Dami, Jeongyeon is a siren-like mermaid and Jinho has become a small fairy or angel.
The only two left untouched are Kyunghwa and Shinwon.

A powerful shapeshifter named Jin Yong-sun takes the form of a dragon and stalks the group. But before long he turns his back on them and abducts Taeil, planning on using him as a sacrifice for the real reason that they were brought to Jeju.