Monstro (2016)

Both of series have the same main actor Kang Ji Hwan, who will return to take vengeance toward the people who wronged him.

Literally the exact same show. They're both bad and both are sure to leave a bitter taste in your mouth :).

Monster has Jo Bo-Ah and the setup is decent, which are the only good things to say.

both main characters are sent to jail for a crime they didn`t commit and try to prove their innocence

has the same type of investigation type show. the main characters are rich or from a rich family. has revenge story theme

Aside from the first 4 episodes of Monster, they're pretty much the same: two guys competing against each other, one being the illegitimate child of the company head, and of course one girl both are interested in.

When I watched Gong shim I kept thinking that it was a little similar to monster.

Similarities:
- in Monster both leads are lawyers and in gong shim the ML is a lawyer
- both have a mystery solving plot line

I want to say Monster is more about revenge and has less scene that are romance.

Both of these dramas start from a similar point, a young rich heir who seems to have everything going in his favor is thrown into dark despair and pain due to a relative's destructive greed. The kids narrowly escape, but return years later harboring secrets to realize their revenge. While both of these kids, now turned men, are ultimately seeking revenge, they display countless acts of kindness to the people around them. They both also use a sense of humor and disarming smile to hide their grief and pain. The leading ladies are both strong, smart women who have lead troubled lives but love their mentally challenged, poor family more than their life. Monster and Can You Hear My Heart have addictive plots with emotional depth and character.

both main leads were traumatized by the villain who killed both parents, and they grew up with the idea of revenge in mind

Both of series have the same main actor Kang Ji Hwan,with double identities and vengeance toward the people who wronged him.However, he finds love on his way. Both stories are smartly-written revenge plot that will keep you hooked from beginning to end