Masks are spooky: they dehumanise, they make a dangerous inhuman inner being visible. White masks occupy a special place. They have a long history in several cultures. Being white, they are blanker and scarier, offering nothing for the eye to hold on to. And look like skulls.
Sometimes our imagination will dwell on what is under the snow-pure mask: ghastly disfigurement? Nothing at all?
Bonus points if the rest of the character is dark to accentuate the mask. Being white it'll show bloodstains starkly.
Note that the mask doesn't have to be pure white; any mask that is paler in color than most human skin tones and relatively featureless fits this trope.
Anime and Manga have noh masks to draw inspiration from. Western tradition has Greek drama masks, the birdlike masks worn by medieval plague doctors (see the Real Life section), scary clowns, The Klan (although their leaders often wear red robes and masks, just like the medieval penitents they eerily resemble) And Venetian Carnival masks. Mexicans have the masks of Dia de los Muertos.
This trope is fairly widespread in Anime and Manga. Compare Cool Mask. Sometimes doubles as a Mask of Power. Subtrope of Malevolent Masked Men.
See also: The Blank.
Tenchi Muyo! - Kain in the first movie has one of these which is also an Expressive Mask, since it turns out to be his real face. It becomes more creepy as he becomes more desperate in the final battle.
Noh-Face from Spirited Away. Noh-Face is first encountered as a partial black cloak and a white mask. Later his body grows a horrible maw, jarring with the lost-child-in-pain expression of the mask.
Death 13 from JoJo's Bizarre Adventure is a dream-haunting clown-themed Grim Reaper that wears an incessantly smiling clown mask. actually that may not be true, since that is more than likely his face.
Soul Eater - Lord Death had a simple skull-shaped mask he made to deliberately avoid looking scary to the small children he wanted to recruit to his school. He added a sillier personality to match, which he took to very well in the long run. His older, much more skull-like mask is doomier. Kid occasionally copies his father's appearance with a cloak and mask of his own. But in his case it just looks cute.
Played with with Kuze in Ghost in the Shell: Stand Alone Complex. Though the face of his white-skinned cybernetic body has been custom sculpted by a famous artist, it has no facial muscles and Kuze doesn't even move his mouth when speaking, so its perfect beauty is always maintained and never twisted.
In Code Geass, Shirley's nightmares are plagued with these◊ in an episode of R2, when she regains her memories and realizes that a lot of people are lying to her. As well, the metaphysical mask◊ found in C's World can be considered a case of this, as it represents the masks that people wear (read: lies) caused by being individuals. It resembles the masks that Shirley had nightmares of, although this was coincidental; the masks were simply a recurring theme.
The Norza in Red Photon Zillion.
In the latest Golgo 13 anime, a cult leader named Gabriel wears one of these. Beneath the mask... well
Yu-Gi-Oh! 5Ds: Aki Izayoi/Akiza Izinski in her Black Rose Witch/Black Rose persona.
Kurei from Flame of Recca always wears a mask when going into battle, and has worn three different ones over the course of the series. What's under his mask? Nothing really, just a badass-looking scar.
The villain Gargoyle in Nadia: The Secret of Blue Water wears a white mask all throughout the series, making an already terrifying character even creepier. We never see his face until the end of the series.
Bloody Monday: Last Season has terrorists in white masks crashing international gathering of dignitaries. Fortunately the masks help the counter-terrorists infiltrate the group; unfortunately the counter-terrorists don't know about the special paint that could be seen with the masks' lenses.
Halloween: Michael Myers, the killer from the movie series wears a spooky white mask. The original was a Captain Kirk mask, bought for all of $1.98, painted white and modified. In the film it doesn't look much like Shatner.
Used symbolically in Ingmar Bergman's The Seventh Seal. Two of the characters (ironically, the only major characters to survive the film's ending) are a husband-and-wife team of actors who perform shows in the streets of the towns they visit while wearing stark white face paint so glaring it shows up even on the film's black-and-white palette. We get to see one of their performances, which consists largely of them singing and playing Bawdy Songs while wearing the whiteface. Their songs, while ostensibly entertaining, are quite crude and sound a bit...off, suggesting that something dire is about to happen. And in fact something dire does happen - namely, the show is interrupted by a procession of flagellating penitents wreathed in incense, loudly moaning Dies irae, dies illa, solvet saeclum in favilla... (which in English is "Day of wrath, day of mourning, Earth in smoldering ashes falling...").
The face-concealing Stormtrooper helmets. It's interesting that the visually similar good-guy Clone Troopers of Clone Wars have color added to their helmets, and are forever getting the mask off to show a human face.
General Grievous sports a white mask in the form of a stylized, elongated skull.
According to the EU, Grievous' mask is ACTUALLY a skull, just not one of a sentient creature (It belongs to a Kaleesh predator).
Early concept art for Darth Maul featured one of these.
The Death Eaters from Harry Potter, in their secret society / magical terrorist mode.
The Stranger in Pallid Mask mentioned in Robert E. Chambers' The King in Yellow short stories, and in Thom Ryng's Defictionalization of the titular play appears to be wearing something like this. The key word is appears.
The Stranger: I wear no mask.
In C. S. Lewis's Till We Have Faces, the protagonist Orual spends most of her life wearing a white veil, which is portrayed in the illustrations as a white mask, completely featureless save for two eyeholes. While she's not evil per se, her subjects are definitely put off by it, and rumors spread about what she's hiding under her veil.
In the Discworld book Masquerade, the Opera Ghost wears a white mask which the narration consistently describes as "like the skull of an angel".
Buckethead is famous for wearing an expressionless white mask and KFC bucket (or plain white plastic bucket) on his head during all performances, as well as just about any public appearance. This is because Brian Carroll happens to be extremely shy and eccentric in spite of his talent, and creating the fictional persona of Buckethead lets him remain semi-anonymous and unrecognized without the pressures of fame.
One of the few publicity photos that David Bowie has done for The Next Day shows him in an ominous white mask.
Death Jester Eldar Aspect Warriors wear skull-masked armour. The twist is, the bones on their armour come from its previous owners.
The assassins of the Eversor temple wear a similar white skull helmet. Where as the other temples of Officio Assassinorum rely on stealth, accuracy, misdirection, and soul crushing power, Eversor Assassins will crash through a wall and kill everyone in the building.
An Eversor's mask looks like a giant skull. It pumps a stupendous amount of combat drugs directly into the brain; the wearer becomes a screaming ball of death and terror. The assassin will kill until he is killed or there is no one left. At which point he explodes.
In the original Phyrexia the holiest symbol beside the phi was the Mask of Yawgmoth, a white mask bearing a twisted expression of sorrow. Several Phyrexian creatures featured the mask somewhere on their bodies.
Several followers of the Lying Darkness wear such masks to denote their status as one of The Blank.
Fu Leng used to wear a white porcelain mask when he had a corporeal form. In some artwork so does his most faithful disciple Daigotsu.
Similar masks are used by Bloodspeakers to animate zombies from the bodies of the dead.
White porcelain masks are also quite in fashion with necromancers such as Iuchiban and Kuni Yori.
The Phantom of The Phantom of the Opera though unusually the Phantom's mask covers less than half of his face. Even though the iconic white half-mask is famous from a thousand theatre posters, in the original novel his mask was black.
Yume Nikki - "Hey, I wonder what this light switch do-aaaaaaaaaaaaaa!"
Averted with Mask*DeMasque in Phoenix Wright: Ace Attorney. He wears a white mask but is generally gleeful and makes himself publicly popular despite being a criminal. Except for when he murders people. But he wasn't wearing the mask at the time and he wasn't the real Mask*DeMasque, so it's still an aversion.
Members of the Masquerade wear these in Persona 2. Generals in particular have theirs styled after the Zodiac sign that doubles as their codename.
The White Glove Society of Fallout: New Vegas all wear White Masks (seen here◊) since it makes them mysterious in the eyes of their leader Marjorie. However, everyone else thinks that it just makes them creepy. Granted, they don't exactly have a clean record, but that's in the past.
In the adventure game Gray Matter, Dr. David Styles, reclusive scientist and resident of an Old Dark House, wears a white mask that covers half his face, reminiscent of the one the Phantom wears, to hide the horrible burn scars that he sustained in the car accident that killed his wife.
The appropriately-monikeredMasked Man in Rune Factory Oceans wears a creepy white mask with a black robe to conceal his appearance. He keeps the mask even after removing the robe and making his identity obvious to the player, only ditching it once he thinks the fight is won.
Curiously for a game that is all about masks, The Legend of Zelda: Majora's Mask only features one. The Couple's Mask also subverts the usual creepiness by being a symbol of marriage and loving union; the lines it has in lieu of a face are a simplified image of an embracing couple.
The Princess and the Frog has Dr. Facilier wear a Baron Samedi half-mask, but only during the climactic moments of his Villain Song. note He's also seen wearing a grinning jester mask while incognito at the Labouff's masquerade ball.
The Adventures of Mark Twain - In the ever-popular (and creepy) "Mysterious Stranger" clip, Satan's face is a Greek drama mask that morphs into various faces, including an exceptionally disturbing skull.
Plague doctors during the Black Death wore white bird masks to prevent from getting the plague. These masks also had the effect of being terrifying◊, despite being a dead ringer for the Black Spy from Spy vs. Spy. For some plague victims, that would be one of the last sights they'd ever see. Being scary was intentional — the doctors had to be fearsome and barely-trusted, half mythical figures, or else they'd get mobbed by the sick every time they went out. They also went armed with clubs. The "beak" was stuffed with sweet smelling herbs to mask the sickening smell of dying plague victims.
Strangely enough, the mask and the rest of the plague doctor outfit actually functioned as a fairly effective, though crude, biohazard suit. Since the mask covered the mucous membranes—eyes, mouth and nose— and doctors covered their bodies entirely with long, waxed robes, they were generally protected from plague spread by fleas or the victim's bodily fluids. Certain herbs in the beak also worked as natural antiseptics (phytoncides), doing a decent job of killing airborne microbes.
The Guy Fawkes masks worn by Anonymous members and some Occupy Wall Street protesters.
Serbian noise musician Dead Body Collection adopts this as part of his stage act.
YouTube gamer Cryaotic is often depicted in fan art as wearing a rather nondescript white mask, as he has never shown his face on camera. Some fans have taken to giving the mask a horror twist with cracks, sharpened-toothlike features, and blood splatters.