I'm not sure there are very scary Kdramas...

I like The Guest. It's not very scary but the ambiance and the story are really good.

Hmmm it's not really horror - it's a psychological thriller - but I think the only K-drama that actively had me on the edge of my seat because I was scared was 'Save Me'. 'Sweet Home' is another, but I wouldn't say I felt scared while watching, just more dread and unease since it has that gory dystopian flavour to it.

'The Guest' and 'Strangers from Hell' are another two that I've frequently seen in recs for unnerving/creepy/scary kdramas, but I haven't seen them myself!

Or, if I was to suggest a movie - Train to Busan had me freaked out for most of the run time.

I stay away from paranormal stuff since it scares the hell out of me.

SAVE ME would be my pick. It’s about a cult and how cults can gain power through control, fear and subjugation. How they prey on the ‘weak’ and bribe their way so as to remain ‘under the radar’. I felt for the FL and how suffocating it was to witness her family be indoctrinated into this cult. Watching her trying to escape was heart pumping and honest to god scary at times.

Cults are real and for me that’s the most frightening aspect. Their ability to brainwash hundreds and thousands of people to follow uncritically is terrifying. The striping of agency and autonomy of an individual and the harsh consequences if a member decides to leave is spine-chilling to say the least. This drama sticks with you because it’s that panic inducing and stifling. Watch at your own risk…

Mouse
White Christmas
Silent Sea
Strange School Tales

and there was a drama with an excellent female villain who was pure evil but I dont remember which drama. it was pretty recent.
then, there is the chilling congresswoman character in Pinocchio

a lot of dramas have creepy scenes like I can hear your voice (the phone ringing! still haunted!) or the granny ghost & one shoe ghost in Masters´ Sun

If you've seen and liked 'Hellbound', you might like 'Cursed' as it was written by 'Train to Busan' and 'Hellbound' writer/director Yeon San Ho. I'll hold off on any comments so I don't spoil any of it, but I'll say it's quite interesting. It even has a movie sequel 'The Cursed: Dead Man's Prey', which I also enjoyed.

Kingdom
All Of Us Are Dead
Save Me

A movie suggestion:

THE DIVINE FURY - MMA fighter Park Seo-Joon helps Catholic priest Ahn Sung-Ki exorcise evil spirits, the most terrifying being the snake demon possessing Woo Do-Hwan. Not a masterpiece by any means, but an entertaining and suspenseful watch. And did I mention—Park Seo-Joon and Woo Do-Hwan?

STRANGERS FROM HELL is not really scary (only a few scenes), but mostly quite disturbing. I can absolutely recommend it.

The two Kingdom seasons.
Connect. I was so shocked this was Go Kyung-pyo's next project after Love in Contract.
Monstrous.
Hometown. You have Um Tae-gu, Han Ye-ri and Yoo Jae Myung here. If you know the repertoire about Um Tae-gu, you should try this one out.
Strangers From Hell. Lee Dong-wook really sold his villain acting chops here to the perfect t.
Hellbound.
The movie - The Call. Scared the hell outta me.
And another K-movie - Confession. This has no right in your face horror, but it is creepy.

I was recently watching a Youtuber cower in fear while watching the premiere of Hotel Del Luna, as though it was the most frightening thing she had ever seen. It was charming to watch.

I watched another Youtuber cower in fear watching the premiere of All Of Us Are Dead. That reaction was a bit more deserved.

I didn't watch Sweet Home but the clips I've seen would qualify it for the list.

I watch a whole slew of scary dramas just recently, and these two are the ones that I consider to be actually meaningful and worth shitting my pants for: Dark Hole and The Guest. The other ones are more brainless horror: All of Us Are Dead and Happiness. They scare you and make you uneasy for no good reason. At the end you just feel relieved it's over and empty. However, Dark Hole and The Guest had good messages, and they felt less like junk food but chicken soup for the soul. Also, the leading actors were hot as hell. If you're gonna walk through the valley of death, you definitely want a handsome man leading the way.

I don't remember if Awaken was scary, but it was definitely creepy.

White Christmas

Lol I named my non-login comment username "Cozybookstoolazytologin" and it wouldn't let me post... it said it was detected as Spam. Logged in it is then, I guess!

I second Hometown as a good one... and I also liked Monstrous as a good ominous drama. Dark Hole gave me a few proper scares as well.