Both involve MULTIPLE RELATIONSHIPS, psychology and comedy-darkness blend.

In KMHM there's 7 characters/7 relationships due to male leads multiple personality disorder; meanwhile in Love Shuffle there's several different relationships due to a group of people deciding to "shuffle"/swap relationship partners with each other multiple times, to test if there exists such a thing as "soulmate"/one person that's better for you.

While both have multiple relationships, both also have a couple of rootable MAIN couples/OTPs with a good romance arc; making shipping easier, while keeping the complexity of the relationship/s and story in tact!

Recommended for fans of psychology, drama-comedy combo, deep and complex characters and story and believable OTP/romance.

Both high quality dramas that deserve a better rating on MDL.

Multiple people involved in a relationship with one person...:

In KMHN 7 personalities/characters due to multiple personality disorder, played by one actor; meanwhile in TBI 21 actors playing one and the same character!

Oh, and both have one actor in common: Park Seo Joon.
In KMHM he plays the 2nd lead character, in TBI he is one of the 21 actor/actresses who plays the male lead character.

Psychology and mystery. Both involve the complex relationship between a psychiatrist and their client. There is a twist at the end of both.

KMHM is a korean drama, while TGH is a chinese film.

Warning: not much/no romance in The Great Hypnotist. Watch it for the psychology and mystery.

Mystery and multiple people involved. In Kill Me Heal Me, these people are the various personalities of the male lead who has mutiple personality disorder; in Mysterious Summer the mysteries surround different people as it is an anthology series with different leads each ep.

KMHM is a korean drama, while MS a chinese drama. Recommeded chinese drama for people who don't even normally like chinese dramas (I'm one of those people)!

Recommended for fans of original mysteries / not just an ordinary detective story!

Psychology and mystery themed fiction. Both play on the mystery relationship between the leads.

Green Tea is more conversational/dialogue-based, less happens; KMHM has a bigger journey/more happens...but regardless both give their take on psychology.
Green Tea is a chinese film, while Kill Me Heal Me is a korean drama.

There's more similarities between these two besides the very similar poster (lol)...
Both mystery romances, with a chaebol/luxurious life backdrop. The male lead in KMHM must hide his multiple identity disorder from the rich, while the female lead in Mask must hide her true identy as a poor woman from the rich.
Similiar melodrama vibes

YOU! WHAT ARE YOU DOING NOT WATCHING THESE TWO!?! You're missing something great...

Both psychology themed and will make you think. Both deal with human darkness and tragedy: Love Shuffle in a way that will make you laugh and think; Memories of Matsuko in a way that will make you cry and think.
Both MUST WATCH. WATCH THEM NOW!

Psychology, depth, introspections featured in both. Same experimental and psychedelic athmosphere. Comedy with bitter darkness and biting black humor.

Fukatsu Eri No Black Comedy (short series, 20 eps x 3-10 min) will make you LAUGH about the absurdity of life, while Memories Of Matsuko (film, 2h 10 min) will leave you CRYING for over half of the film!

Both are essentially comedies but with underlying darkness, bitterness and depth. Psychology genre with introspections over humanity, life and love.
Recommended for fans of depth, psychology and/or dark humor lovers or just people with an overral cynical outlook on life and humanity.

Love Shuffle is 10 eps x 45 min,
while Fukatsu Eri No Black Comedy is 20 eps x 3-10 min

-Both include the love story between a Grim Reaper and a mortal human
-Both have a group of grim reapers doing their duty, in so, deal with life & death questions
-In both the Grim Reaper character is cute, unique and very lovable

In Universe's star the Grim Reaper/Human lovestory is the main focus/main OTP, in Goblin it's only a secondary leads/second OTP story.

-Both are tear-filled ROMANCE MELODRAMAS where the leads know each other for years and struggle to get maybe together
-Both have EXCELLENT main pairing with great CHEMISTRY