Jagged Mouth

Many monsters appear in media, and they all take on different forms. Their mouths are no exception as they can make creatures disturbing or scarier than they would be if they had normal mouths. This is a simple version of that where a creatures mouth-line is represented in a zig-zag pattern. this is a good way to show how twisted a creature could be, unless the monster turns out to be nice, in which case it is Dark Is Not Evil. Following that insanity rule, this sort of mouth can be done in a few versions.

The mouth is a zig-zagged line but isn't as sharp as it could be, hinting at an animal-like nature ( I.E. many heartless from Kingdom Hearts apply)
The mouth looks very sharp looking, or is very long hinting at insanity. both can usually end in a Goth Spirals at either end of the mouth for Rule of Cool.
This sort of mouth can appear in two varieties; the first is in a character's sillouhette, showing how sinister they are while they are in the shadows, this smile is used alot with the Glowing Eyes of Doom. the second is when it appears on a person's shadow which has the same effect and can be used for the same purposes. this especailly works well with characters that don't have jagged mouths in the first place.

Compare and with Slasher Smile, where the character's feature could have the same affect, but it does not nessecarily mean they are evil. Not to be confused with More Teeth Than the Osmond Family, where the charcter's teeth could be serrated, but the mouth line outside is striaght. Compare and Contrast Bizarre Alien Biology, where the mouth line could be serrated or zig-zagged for instance, but could have a different function or place on the body, sometimes mixing this trope with Belly Mouth.

Examples :

Anime

Many monsters in Digimon sport this sort of mouth type.
Some Yu-Gi-Oh! monster use this trope

Video Games

Nearly all heartless from Kingdom Hearts, as well as some nobodies have these
- Some dream eaters from Dream Drop Distance are examples, most notably one that looks like a Dodo or a dragon that has a large mouth on it's main body.
Various Final Fantasy enemies
Doctor Lautrec and the Forgotten Knights" has Treasure Animatis that sport these. mostly in their feral forms.
Chillion From Zack and Wiki
Water Glaboros from Kirby's Return to Dream Land

Web Original

Atop the Fourth Wall has the Entity Missingno. portrayed with this sort of mouth in the The Electric Tale of Pikachu title card.