Both are short cutesy web dramas which involve body swapping between a celebrity and a normal person.

Both have superhuman powers, set in school, fighting against forces bigger then the local bully and also have a similar sort of feel to them :3

Both are about people who go back in time and become important people. Both have tragic love stories.

Both are about correcting mistakes of the past, they show how life choices can change your life but it's not too late for a second chance.

Both about the making and debut of an idol band containing men with troubled pasts. Both have big labels trying to stop them.

Both about 'ajumma's who had mistake marriages because they got pregnant and decide to take their lives back. Both also have shallow cheating husbands.

Both are short web dramas about two people falling in love over Line, whilst speaking little or none of the others language.

Both films are set in an all boys high school, where all the boys are sex obsessed and slightly perverted. An attractive female teacher joins the school and its seen as a sex icon for the guys. Both have a student falling for a teacher.
Wet Dreams is about a group of guys learning about sex; expect crude humour, bad jokes and lots of innuendos. But it is quite funny (bad to the point of being good).
Who Slept With Her is about a female teacher who acts super sexually and its misunderstood to have slept with a student. Again, expect bad jokes, perverted boys and innuendos. Still had funny parts though.

Both have a girl dressing up as a guy to go school in around the Joeson period. Both contain two people falling in love blah blah.
Snow Lotus is a lot shorter and contains past as well as present, all about reincarnation and loving people and dreams.
Whereas Sungkyunkwan Scandal is more focused on the girl dressing up as a guy and going to school, entirely in the past.

Both are about pop stars who have flopped out of the industry and are living their lives.

Both are about women who are dumped by their superstar boyfriends. Skip Beat! is more about revenge against ex-boyfriend, whereas Lovesick is more about getting over ex-boyfriend (kinda).

Both are about housewives who realise after years that they can actually chase their dreams before it's too late. Second Time Twenty is a little more serious then Niriko I think, but they are both very sweet.