Curiously, each Mouth Monster is found wandering around near a blood splatter (the same one seen in Eyeball World and the ending). What this represents, as with everything else in the game, is a mystery. No Mouth Monsters are ever seen where there are other types of NPCs in the vicinity. The implication may be that they have eaten another creature and wear their hair as a trophy, which perhaps explains why Madotsuki can take it off them.
The Poop Hair Mouth Monster is a little different from the others. Not only is it found in a separate location than the other two, but its behavior is slightly different, too - it will always move towards Madotsuki, whereas the others move randomly. Additionally, the Poop Hair effect has a different action than the other two, it creates flies to be used as landmarks in a location.
All three give effects that change Madotsuki's hairstyle when interacted with:
- The one with brown hair gives the Long Hair effect.
- The one with blonde hair gives the Blonde Hair effect.
- The one with the hairstyle that looks like a cartoon poop gives Madotsuki the Poop Hair effect.
- It is possible that the Mouth Monsters are based on a youkai called a Futakuchi-onna, which is a woman with a large mouth located in the hair at the back of her head.
- In older versions of Mural World, all three monsters were found in the area due to Underground World not yet in the game, making it the only place to house three effects.