Recommendations

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

I feel there are many similarities between these 2 dramas. Both have successful actor and a rising actor as male leads. And I feel like there are other similarities.

Both dramas are time travel dramas where someone (or multiple people) travel back in time. They are both set in the modern time, but go back to the 1990s, which could maybe impact the future...
Both stories are focused on high school and friendship. They both have romance and bromance, but also deal with some heavy topics.
Differences are in the focus of the story, the way they could time travel, and the genre:
Whereas Twinkling Watermelon is much sweeter and has some comedy in it, Someday or One Day is a thriller. They also end very differently.

These are both action-packed shows that start off with the character having a hard time because their character development hasn't kicked in. But as both shows go on, you start to see the dominance, and the vengeance starts to grow in the characters.

While Big Mouth is a husband-and-wife duo that starts off having the ML cute and flexible but not successful at all, while the FL is trying to support them both... As the show progresses, the ML starts to face challenging situations that refine his overall character. The ML has one of the biggest changes in character I have probably ever seen in a show, and there is never a dull moment because of it!

Big Mouth also seems to have two plots going on at the same time: the main plot that the ML is tangled up in and the subplot that the FL is working on. But both of these plots end up crossing each other in unexpected ways, causing the show to be an absolute masterpiece.

you should watch TBNW first as the other one is a special extra epsisode with a light story, fluffy, some kissing and a bit fan-service, there isn't anything surprising but still, it is cute overall, with the same good chemistry between the actors :)

‘Accidental’ marriage/marriage of convenience
(Very loosely used here)

He fell first but she fell harder.

Have some time of history before ‘first’ meeting.

Very cutesy scenes.

Dan Bi is a high school senior who has given up on math. On the day she is about to take the KSAT for college, she is transported back into the past during a freak rain shower. She finds herself hundreds of years in the past at the height of the Joseon Kingdom, which is suffering from a severe drought. She encounters King Lee Do who yearns to learn advanced mathematics and falls in love with him. This is a romance that transcends space and time with two lovers who come to know each other on a deeper level.

Crown Prince Yi Gak finds that he has been transported from the Joseon Dynasty to modern-day Seoul. He meets Hong Se Na, who bears a striking resemblance to his dead wife, and is determined to solve the 300-year-old mystery of her death. With his own resemblance to the CEO’s grandson at the company where Se Na works, Gak assumes the identity of the young man to stay close to her. Can the Crown Prince navigate a modern corporation to find clues to his own time period

Ma Gwang Suk works as a section chief at the Shiwan Post Office. She is 45 years old and single. She meets O Jang Su, who is CEO of Eagle Brewery, and they decide to get married. But, only 10 days after their marriage, O Jang Su gets into an accident and dies. Ma Gwang Suk takes over the brewery and becomes the breadwinner for her 4 younger brothers-in-law. She has a cheerful and lively personality, which helps her persevere.

Han Dong Seok is the chairman of LX Hotel. He was born into a wealthy family and has never lacked anything, but having lost his wife 15 years ago, he lives his life in loneliness. He is also arrogant and has a clear opinion on what he thinks is right or wrong. He meets Ma Gwang Suk.

This is for the special edition, the same story and the same exact cast, and this is for the extra- Due to an unforeseen situation, a naive freshman and the campus’s popular senior agree to pretend to be a couple—but their fake deal begins to affect their real feelings.

Is the uncovers, same story. Due to an unforeseen situation, a naive freshman and the campus’s popular senior agree to pretend to be a couple—but their fake deal begins to affect their real feelings.

Both dramas tell stories about complicated relationships. "My Dearest Nemesis" seems to be about people getting over bad things that happened to them and growing as people. "My Sweet Mobster" seems to be about a man trying to be good after being bad. So, if you like shows with people who have old relationships and change a lot, or if you like shows about childhood relationship, you might like both of these dramas.

Both dramas have FLs who are smart, business-savvy women in the male-dominated steel industry of 1980s China. Family-friendly dramas. Both excellent.

Similar era—1980s. Both stories show the development of the leads from their humble status to business leaders.

Both dramas are great makjang, complete with birth secrets, angst, murder plots, and revenge. One difference is Hotel King has more romance, but the revenge plot is still the driving force of the story.