Monster Mouth

Losing your entire jaw really bites.

A standard way to make monstrous figures appear alien is to mess around with their anatomy in ways that are "atypical" (to put it mildly) of human beings or, more broadly, most real-life animals.^note One such trait that always looks menacing and foreboding is the mouth, whether by giving it an irregular or distorted shape, making the teeth within it look hideous or terrifyingly deadly, putting it somewhere where it logically should not be, having there be more than one, or a number of other methods.

Can be a Sub-Trope to either Bizarre Alien Biology or Body Horror, depending on whether the mouth in question is "supposed" to look like that. Frequently occurs in conjunction with Nightmare Face. No connection to Facial Horror, as that trope deals with injury and disfigurement. See also Good Lips, Evil Jaws.

NOTE: Please only list examples that do not fit neatly into one of the Sub-Tropes.

Examples:

open/close all folders

Films — Live-Action

The Reapers from Blade II have type three Monstrous Mandibles that hide a protrusile Flower Mouth via Nested Mouths.
Godzilla vs. Kong: Mechagodzilla has intimidating-looking jagged jaws, which themselves contain rows of buzzsaws designed to violently tear through the hide of any Titan that Mechagodzilla bites down on (although we never see the Mecha using them in combat).

Literature

Gugs are a very strange monstrous race in The Dream-Quest of Unknown Kadath, with unsettling mouths that run vertically, rather than horizontally, across their faces. This is perhaps their most distinctly weird trait, but not the only one.
In The Scar, the Anophelii are a species of humanoid "mosquito people" whose females' jaw hides a thick, foot-long, blood-draining spike. Their all-consuming Horror Hunger and the atrocities of their short-lived "Malarial Queendom" make them infamous even in the Crapsack World of Bas-Lag. The males, however, have toothless, sphincter-like mouths, and are rather silly-looking to a human visitor.

Live-Action TV

Star Trek:
- The Nausicaans, a race of brutish mercenary thugs, are easily recognizable for their wide, upside-down "V"-shaped jaws with exterior teeth.
- The Kradin, who resemble Nausicaans with even more teeth.

Video Games

Amnesia: The Dark Descent: The Grunts' mouths are split open down the length of one cheek and their jaws are allowed to hang freely.
Dead Space: Among the many changes they undergo, the most striking characteristic of Necromorphs are the protruded jaw lines.
The Cabal species in Destiny all have natural, teeth-baring lip clefts◊ under their helmets, making their default expression a snarl or sneer.
In Legacy of Kain: Soul Reaver, Raziel has no lower jaw.
In Halo, the Elites — or "Sangheili", as they call themselves — have a relatively ordinary upper jaw, but what they have in place of a lower jaw varies by franchise installment: sometimes it's a double set of type 2 Monstrous Mandibles, sometimes it's one half of a Flower Mouth, sometimes it's somewhere in between.
Mass Effect:
- The Elcor have mouths consisting of a series of vertical slits reminiscent of shark gills that wiggle up and down as they speak.
- The mouth of a Thresher Maw seems to consist of four long tendrils surrounding a tentacle-like, un-retractile tongue.
In Minecraft, Endermen have mouths that raise their entire upper head when opened, making their mouths see-through.
Gryftrot and Photoshop Flowey from Undertale both have a mouth that takes elements from both Vagina Dentata and type 2 Monstrous Mandibles. More specifically, take the process by which one turns a human mouth into a vagina dentata (rotating it 90 degrees) and apply it to something like an alligator or horse's mouth.

Webcomics

Web Videos

Alien Biospheres, being dedicated to the speculative evolution of a planet of Starfish Aliens, features all sorts of wacky chompers.