These two dramas have very similar plot points. Most of them would be spoilers, but in both dramas the ML has to hide his very obvious love for the FL from the other people surrounding them (and in both cases it is both for the mission and FL's sake).
And the romance follows pretty much the same structure with many similarities to Romeo and Juliet.
Seriously, watching Snowdrop has brought me so much nostalgia from Bridal Mask!

Both shows are about the k-pop group INFINITE and they dive into different aspects of the group's dynamics.