Recommendations

The serial killers aren't similar, in fact Door Lock kind of has a lame ending, but 80% of the movie from the beginning is very interesting, both have a lot of suspence, feel threatening and both female leads end up killing the killer in the end.
In 'Door Lock' the serial killer is more gruesome.
In both the killer is obsessed with the female protagonist - but in 'Somebody' it's love, while in 'Door Lock' it's just another victim of stalking, obsession and not 'united by murder' at all.

Midnight is a movie about a serial killer who stalks a handicapped, yet very determined and clever girl. The serial killer, played by Wi Hajoon is very similar to Yuno in 'Somebody'.
Both have a plotline of a handicapped girl being tormented by serial killer - in 'Somebody' the girl is in a wheelchair, while in 'Midnight' she's deaf and has to get away from her assailant using wit.
Both serial killers are psychopathic and have a few endearing moments with the victims.
Both girl leads get revenge on the killer.
Both are suspenceful.

Not the same plot or theme, but Reply has Choi Taek who's also a genius Baduk player. In Reply, you can see the dilemmas of being an "undefeatable" Baduk player to going on a slump and then making a comeback.

-Both are Bls
-Both are based on omega verse
-Both have characters who conceal their identities

After stumbling on a device that can make other people disappear, a man and woman entangled in an affair devise a plan to start a new life together.

A mysterious, clever girl named Nanno transfers to different schools, exposing the lies and misdeeds of the students and faculty at every turn

Similarities: a supernatural being infiltrating the school and exposing lies of cheaters and those who commit sins in a sinister cat and mice game.

Sequel to the second season

Female lead is non-chalant, not cringy, sacrificed herself for her family. She didn’t chase so called love line, because she was too busy with her revenge and her own life. But chemistry with ML is something you can feel to the bone. FL never said that she loved ML, but deep down she always waited for the ML.

- Both FL is rumored as evil/demon.
- Both FL forcefully takes ML as her disciple.
- Both FL has multiple male disciples.
- Both ML first hated the FL and slowly falls for her after finding that she is kind hearted.
- Both ML protects the FL.
- Both FL loses their memory after some accidents and forgets that they were master of the ML.

Both dramas involve a lot of action and some vigilante justice. There are knives and good action scenes involving them, and also a lot of mobsters doing their thing.

Pretty interesting MCs in both stories.

Both dramas involve lots of gunfights (and some knife fights so far). Both MLs are retired soldiers (or mercenaries) and they didn't forget their training. Both dramas involve sidekicks who aren't what they seem to be.

Pretty good action, overall. Some interesting character portrayal, too. Recc'ed!

Both dramas were romance fantasy. It is set on historical setting and has supernatural and wuxia elements.

FL transmigrated to story and ML is cold-blooded prince . FL changed the story after being in the story's world.

Both of the FLs come from the sea and begin living among humans in disguise. Surplus princess was cancelled early, so it has a rushed ending.

Both FLs are under a curse that causes them to shift either their souls to a stranger's body or shift their appearance, appearing as different people.