Here is the full list of all 30 Lady in Mystery achievements.
You've met the one who can change your destiny.
Arrest the suspect on episode 2.
You've asked the pale worker on episode 4 why he can't look at the blood.
Seoyeon gave you a Seonchu as a gift.
Heesoo has sung a song greatly.
You've cleared all the common episodes and now reached the the point where you can choose your own episode.
Kang Yurin came in to your room.
You've seduced a woman in afterlife.
You've answered more than 3 times with the word that didn't exist in that time period.
You've died more than 5 times.
Meet the guru at the fortune teller's street.
You've seen Seoyeon feeling seasick.
You've learned Seoyeon's heart of hearts.
You've tried to suppress Juhee's compulsion.
You've been gifted a Fire Bead from Iljime.
You've sold Seoyeon's gift.
A servant girl's love has been exposed.
You've met Heesoo in women's clothes.
You've seen Iljime's wound.
You've made Kang Yurin furious.
You've found Kang Yurin's secret storage.
You've found a strand of hair in Pyeongho's drawer.
You've chosen Juhee over 'Revenge.'
You've seen the true ending of Seoyeon.
You've seen the true ending of Juhee.
You've seen the true ending of Yurin.
You've seen the true ending of Iljime.
You've seen the true ending of the revenge route.
You've seen all 23 of episodes.
You've collected all the endings including bad endings.