The Fades - episode 3

An insecure young man who is developing strange magical powers that allow him to manipulate reality.  An older sister who constantly treats him cruelly.  I think you can predict where this is going...

Charmed - episode s07e08 "Charmed Noir"

 An argument with a grumpy gnome leaves librarian/witch Miss Donovan (Ann Cusack) momentarily mouthless.

Beetlejuice

Beetlejuice is a film about a malevolent ghost named, yes, Beetlejuice. One can summon him from the underworld or dismiss him by speaking his name three times. Of course, once Beetlejuice has been called up, he doesn't want to leave...ever. When Barbara (Geena Davis) attempts to get rid of him, he uses his supernatural powers to shut her up.

House of Wax

House of Wax is a horror movie. I've never actually watched the whole thing, so here's a synopsis from IMDB: "Six friends are stranded in a ghost town where a towering wax museum looms ahead. And inside are two brothers who have a special way of making the wax figures look real... " But that isn't important. What's important is that Elisha Cuthbert has her lips sealed during the film.

Warlock: the Armageddon

The son of Satan is on a quest to collect magic runestones so he can destroy the world or something like that.  One of the stones is located inside the office of an art collector.  The art collector's mouthy secretary makes the mistake of challenging the Warlock's right to enter and well... see for yourself.

Posted by request.

Blood Ties - episode 3 "Bad Juju"

Coreen makes the mistake of interrupting the voodoo-practicing Big Bad of the episode and pays dearly for it.  A quick voodoo curse shuts her up but good.

Buffy the Vampire Slayer - episode 3 "the Witch"

Strange events are occurring at Sunnydale High.  Cheerleaders are being rendered incapable of performing with the cheer squad through various supernatural means.  The poor girl depicted here is knocked out of the running when her mouth mysteriously vanishes from her face.  You can't cheer if you haven't got a mouth, right?