With the ranks of villains being full of such weird and wonderful characters, it's only natural that the subject of unmasking them is one that is never not at least a little bit exciting.
Whenever a masked villain appears, in any format, one of your first thoughts is about when and whether they'll be unmasked, and what exactly may lie beneath.
Not only does unmasking a villain solve the mystery of their true identity - feeding us information we would otherwise never know about these characters - it also often creates new questions, as many villains only become all the more interesting when you finally witness the unusual circumstances that is their face. While you'd initially presume it's almost always a scar or wound, the times it isn't are far more interesting, as seeing writers and artists make a genuinely unique face reveal feels far more special.
And the more creative the better. Witnessing an unmasking create a scenario you'd literally never have expected before - such as realising that Batman has technically punched a baby, or that Deadpool's face resembles a child recreating a human face in chewing gum more than an actual cranium...
10. Black Mask
For a long time, the matter of who was behind Black Mask was not a major one, or one that provoked fan speculation. The villainous identity belonged to the sadistic crime lord known as Roman Sionis, and that was precisely as complicated as things tended to get.
But after Sionis dies, another Black Mask appears - later revealed to be Jeremiah Arkham - and so the plot, unsurprisingly, thickens. It's heavily suggested from this that the actual mask that Sionis and Arkham wear is somehow possessed, as Arkham seems actively controlled by the mask when it is on or even near him.
Whether we'll see the supernatural aspects of the mask be expanded upon at a later date is unclear, as this did take place in the New 52 reboot, and has not seen use since. But as far as fun and surprising unmaskings go, finding out it is the mask itself that is evil is a pretty dang good one.