Mask of Power

The Mask of Power is an object when worn on the face grants the wearer any number of powers depending on the mask itself.

Hey, there's an inscription... *One mask to rule them all, one mask to find them...*Eh. Probably nothing.

Often it will get some backstory to explain its power, whether that's where the power comes from or what sort of power it is. Perhaps it was the facial representation of some deity, or it may have been worn by some ancient ruler or mage, or maybe it was connected to some vaguely defined tropical mysticism. The latter point is possibly influenced by the preponderance of masks in Tiki culture.

Then there's the symbolism of taking upon oneself a new face, the metaphor of looking through different eyes becoming literal as well as the sense that masks are just really badass. However the flip side of the power being in the mask and the importance of the "new face" that can have its own personality is that you can get a literal Becoming the Mask situation, with the mask taking over the character.

Compare Hat of Power, Ring of Power, Crystal Skull.

Not to be confused with Cool Mask, in which a character who wears a mask is assumed to be powerful but does not necessarily have power because of the mask itself.

Examples of Mask of Power include:

Anime & Manga

The Visored in Bleach can increase their power tenfold by calling out their inner Hollow and wearing its mask in battle, the trope is also inverted in that Arrancar -- the polar opposite of Vizards -- are more powerful because they took their Hollow masks off.
- Ichigo's hollow side definitely deserves a mention of its own, because when his hollow form takes over in his epic fight with Byakuya Kuchiki, it started growing onto his face.
Jo Jos Bizarre Adventure has the Stone Mask, which pretty much gave Dio all his powers. A slight variation in that you only need to wear it once.
- The mask had to be worn and then spilled with some blood. Then the mask would sprout some stone tentacles that carved into your brain, killing you but also activating unknown areas of it, bringing you back as a vampire. Also they made you food for the Pillar Men, who created/generated the masks.
In Tajikarao, the eponymous Shinto god is able to manifest physically when a spiritually suitable human puts a sacred mask on his face.
The Cassandra Mask in Ann Cassandra gives its user the power to create evil fates at the price of losing their free will and eventually dying. Supposedly, it was created from the remains of the Greek prophetess Cassandra after she died cursing the people who wouldn't believe her.

Comic Books

Doctor Fate's helmet in The DCU. It even got its own mini-series The Helmet of Fate where it passed through the hands of different mystical heroes before finding its way to its new wielder.
The DC Comics villain Psycho-Pirate got his emotion-controlling powers from the "Medusa Mask" although this is a subversion, as he had to take the mask off (so people could see his face) to use his powers.
The Mask
One of Victory Girl's first opponents was a Mexican "god" in the form of a possessing mask.

Film

The titular mask from The Mask. It's noted in the film that this style of mask is meant to represent Loki, Norse Trickster god, and Stanley hypothesises that the spirit of Loki was banished into the mask.
In the lucha film El Hacha Diabolica, El Santo's mask turns out to be a mystical artifact and key to defeating the villain.
The Halloween series. Especially in the first film; Michael doesn't kill anyone except when wearing a mask. In the intro he only froze when his dad removed his clown mask, and later when Laurie knocks his mask off he takes the time to put it back on, giving her a better chance of escaping. First thing he does before starting his spree is steal the mask, but not for disguise since he never takes it off and few people would recognize him. In the sequel, he still wears the mask (getting an innocent lookalike killed) and is discovered to have scrolled Samhain (basically, Halloween) on the wall of the mask store he robbed, suggesting he somehow links dressing up with murdering people; he becomes the Boogeyman.
The Alchemist from Vidocq wears a mask made out of mirror that he uses to eat the souls of his victims. For extra creepiness, it also makes the victim see their own dying face while looking at him. Extra creepiness: it has to be reforged periodically, and the most important step is tempering it with the blood of a hundred virgin girls.
The titular Mirror Mask. The people of the film believe it created the world, and it certainly has the power to let one escape that world.

Literature

In the Star Trek Novel Verse, the recitation masks of the Oralian Way religion. This Cardassian faith makes use of ceremonial masks which channel the life energy of the wearer, allowing them to become closer to Oralius and the Fates, even at times serve as a vessel for Oralius. Genuine masks amplify empathic and telepathic abilities, essentially being a form of Amplifier Artifact. Some masks are just replicas, though. The Dithparu's mask is a sinister version of the recitation mask. See: Star Trek the Lost Era in particular.
The Mask of the Sun was essentially decoration added to goggles which somehow gave the wearer perceptions of the future, along with hints how to manipulate that future in his favor. The first time the main character put it on, it gave him a vision of himself shifting two pieces of furniture. He did so, and the changed positions of a coffee table and a floor lamp led to the people who attacked him a minute later accidentally shooting one of their own guys, allowing the hero to get away....

Live Action TV

Buffy the Vampire Slayer episode "Dead Man's Party" - the mask of a Nigerian demon, Ovu Mobani (the) Evil Eye, gave its wearers, typically evil voodoo sorcerers, the demon's power, i.e., raising evil zombies under the wearer's control. When the mask was brought to Sunnydale, it began animating zombies of its own accord. It turns out that if one of its zombies is allowed to wear the mask, Ovu Mobani would be reincarnated. And even though Ovu Mobani reincarnated, Buffy soon disposed of it with a garden shovel.
The Mask of Zen-Aku in Power Rangers Wild Force. Grants great power, at the cost of also granting a Super-Powered Evil Side.
- In Power Rangers Ninja Storm, there's the mask that held the spirit of Shimazu. (Fortunately, it was on a statue. Of Shimazu.)

Tabletop Games

Dungeons and Dragons - There are a fair number of powerful mask magical items in various sourcebooks of 3.0/3.5 but in the Complete Scoundrel there also exists a prestige whose soul purpose 'is' this trope. The player gains the ability early on to forge masks of specified types that grant some degree of magical anonymity versus the players alignment being felt out as well as stat bonus' specific to the type.
Exalted has Mask of Thousand Faces that allows the wearer to look like another person. Powerful characters can make items, including masks, that grant powerful bonuses.
Warhammer Fantasy - The Dark Elf pirate lord Lokhir Fellheart has a magical golden kraken mask that he liberated from an ancient underwater city. It inspires unreasoning otherworldly terror in his combat opponents.
- A similar mask - the Terrifying Mask of Eee! - is available in the current (8th edition) common magic items list. It also causes terror, but prevents the wearer from leading troops effectively. The Tomb Kings have the Death Mask of Kharnut, which is even more terrifying, and the High Elves have the Mask of the Merlord, which is not terrifying but does enable its wearer to move through aquatic terrain more easily.

Toys

This half the premise of the 80's toy line/TV series MASK. The other half being transforming vehicles.
Bionicle had Kanohi Masks that granted powers to the wearer (who were usually Toa). In fact, they were a main theme until a Retool, and the franchise could be the Trope Namer as "Masks of Power" was a common name for them from day one. Definitely in the "tropical mysticism" tiki-mask style, as the franchise had a number of Polynesian influences in its earliest days.

Video Games

The Legend of Zelda has a couple of examples:
- The Legend of Zelda: Majora's Mask has 24 masks, and virtually all of them grant the wearer some sort of power, ranging from "one specific type of enemy will talk to you instead of attacking" to "transformation into one of the other races (Zora, Deku, or Goron)" to granting minor abilities such as enhanced speed or invisibility. If you get all the masks by the end of the game, you receive a mask that's an Infinity+1 Sword that turns you into a Physical God and makes the Final Boss fight a Curb Stomp Battle in your favor.
  - And of course, the titular mask itself, acting as a Sealed Evil in a Can that corrupts whoever wears it. It doesn't actually need someone to wear it, though - once Skullkid is of no more use, it fights you under its own power, becoming humanoid in the process.
- The Legend of Zelda: Ocarina of Time has the Mask of Truth, which grants the wearer the power to speak to Gossip Stones. Its other masks, however, don't have any special powers.
  - Keese won't attack you if you're wearing the Skull Mask, which gets especially useful once the Keese are on fire. The Stalchildren won't appear if you're wearing the Bunny Hood. Still, it's a far cry from the Fierce Deity.
- The Legend of Zelda the Wind Waker has the Hero's Mask, which lets you see enemies' HP (if you can figure out how to equip it).
There's also Splatterhouse, whereas by donning the 'Terror Mask', seemingly normal Rick Taylor turns into a Badass with a habit of punching out Cthulhu and every punches turned everything he touches into plasticines. The mask is also alive with a mind too. In fact, it's trying to use Rick to Take Over the World. Though eventually Rick has amassed enough power to kick its behind through a Battle in the Center of the Mind.
The Mask of the Wraith, from Prince of Persia: Warrior Within, allows a person to exist twice in the same timeline.
Gabranth in Dissidia Final Fantasy goes from slow, weak and vulnerable in his normal mode to fast, powerful and deadly in his EX Mode. The graphical change for the two modes consists of Gabranth just putting his helmet on.
- And glowing like the heart of an inferno.
  - And managing to split his double edged sword into two.
Crash Bandicoot has Aku Aku, a sentient mask that gives Crash temporary invulnerability and makes him faster and stronger for some seconds when Crash puts it on. In games like Crash Bash or the racing series, Uka Uka acts in the same way towards Neo Cortex and his team. Also, in Crash Nitro Kart, the "Overlord" of the galaxy, Velo, also acts as a mask for two teams of four racers each, while Aku Aku and Uka Uka serve as the masks for their respective factions.
The Shakalaka from Monster Hunter wear masks both to conceal their faces and also as weapons of war. The King Shakalaka, for instance, can lob fire from the BBQ Spit he wears on his head. Of course, the most prevalent example is Cha-Cha, who changes personality and behavior based on the mask he wears.
- The Ancient Mask enshrined in Moga Village serves as an important item in the hunt for the Ceadeus, as it produces oxygen from the water it takes in. Unfortunately for the Wyverian Craftsman and Junior, all the stuff that makes this possible makes it too small for a human to wear...
God of War: Chains of Olympus has Charon's golden mask, which allows him - and later Kratos when he defeats Charon - to create a green flame that stuns and damages enemies.
The titular mask from the fifth Professor Layton game allows the user to fly, contol gravity, and turn people to stone.
The Elder Scrolls V Skyrim has the Masks of the Dragon Priests, all of which come with a powerful enchantment and a high armor rating.
Dark Souls has Pinwheel, who wears three of them. The player can obtain these masks, each of them offering unique status buffs.

Web Original

This is inverted in the Global Guardians PBEM Universe with the Mask Of Justice. The eyeholeless mask he wears itself is powerless, but he can only use his vision powers while his eyes are covered with an opaque object...such as his mask.

Fan Fiction

The Neon Genesis Evangelion/Zero no Tsukaima fanfic Points of Familiarity has the protagonist create Angel-type bone Masks with very strange properties.

Western Animation

The Mighty Ducks has a mask that gives the wearer the power to see anthing that's currently invisible. It was created by the Ducks greatest hero, Drake DuCain and later worn by resistance leaders Canard and Wildwing. Also, the mask can only be worn by ducks, it tends to shock anyone else how tries putting it on.
In Jackie Chan Adventures there were nine such masks, each giving the user control over one of nine tribes of ninja called the Shadow Khan. It also turns the wearer evil.
Inverted, surprisingly, in Re Boot. Hexidecimal's power is naturally chaotic and uncontrollable - her white mask actually keeps it in check. A single crack made her Ax Crazy, removing it completely nearly caused The End of the World as We Know It, and fixing it (via defragmentation) mellowed her out considerably.
MASK features "masks" (helmets, if you want to get technical about the details) which each have their own powers, ranging from shooting glue to firing blobs of lava.
The villain Catra from She Ra Princess of Power has a mask that lets her turn into a panther when she moves it over her eyes. It also has other abilities, like teleportation and telepathic communication with cats, but she doesn't know its full potential because it was stolen from its rightful owner.