Some examples I liked similar to this is... Healer, Scarlet heart ryeo and ruler - master of the mask

so main hero can be either masked, has a hidden indentity (hes a vigilante at night), or the hero is scarred. I like the mystery in the heroine finding out who he is. Unfortunately there isnt much in this type... any suggestions?

When I think about masked heroes, the first two shows coming to my mind are Gaksital and Iljimae. In both of them, they are fighting for justice with a hidden identity and the girl falls in love with the one under the mask but couldn't guess who he is actually.
I know of The Man in the Mask, but I haven't watched it.
Love O2O is a university / online gamine drama where the heroine doesn't know the top player in the game is the male lead (there are a few identity revelations). 

City Hunter is a bit dark and not as focused on the romance, but the vigilante pretends to be weak / hides his real identity from the female lead. 

In Sungkyunkwan Scandal the second male lead has a hidden sort-of vigilante identity (and the female lead also hides her own identity).
Bridal Mask
City Hunter
Iljimae
Ghost - no romance
Kaitou Tantei Yamaneko - no romance

Hero is a Korean Drama involving a character (the main character) who becomes a masked hero