One of the reasons to wear a mask is indeed to conceal a hideous visage. So if the heroes ever unmask the masked villain, this is one of the potential jaw-dropping revelations you can make.

Another cool thing is if the villain has no face at all. We'll just let that sit there while your brain processes it.

Transcript

Boba Fett: {voice over} "Jango hired my mother, a shapeshifter, to impersonate the Jedi Council treasurer and authorise payment for the army."
Boba Fett: {voice over} "She had me infiltrate the Jedi Library as a youngling, to erase the clone world of Kamino from the archives."
Jocasta Nu: {flashback} Tough luck! All the books about planets were eaten by dogs.
Obi-Wan: {flashback} Um...
Boba Fett: {voice over} "Unfortunately I got caught up in a sparring class, and without Jedi reflexes I was injured in the splanch."
Boba Fett: {voice over} "It crippled my shapeshifting ability and my form stuck."
Jango Fett: {flashback, to Zam Wessel} I'll pay for your kid's operation... if you kill Kenobi's friends with these centipedes. I want to see him suffer.
Han: And now you wear that mask to conceal your hideous visage.
Boba Fett: No! I look like Jango!
Boba Fett: Just like all the clone troopers! It's very confusing!
Chewbacca: Don't the clones wear masks too?