Sinister, wall-dwelling creatures found in Konami's 1991 Super Castlevania IV (original Japanese title: Akumajo Dorakyura, which translates to "Demon Castle Dracula") SNES video game. While all the Wall Widows in said game make their homes inside masonry, in other Castlevania titles (specifically Haunted Castle and Castlevania Chronicles/Akumajo Dorakyura X68000) they inhabit tree trunks and have a more bark-like physical appearance.
The Wall Widow is an ambush predator. She silently waits, never sleeping, until a living creature passes near the patch of bricks and mortar that she inhabits, at which time the monster suddenly lunges outwards, materializing out of solid stone, to attack. They largely subsist on birds, toads, mice, and other small vertebrates, but are always on the lookout for larger and tastier prey, human males being their favorite. While they frequently succeed with their surprise attacks, Wall Widows are permanently fixed in place, so, once a potential victim discovers (usually the hard way) the exact location where the creature hides, they are unlikely to ever fall for the same trick again. As such, Wall Widows must incapacitate or slay their prey outright on their first strike if they hope to feed. These deadly females are also intelligent enough to clean up after themselves, tossing the bones, and belongings, of previous meals as far away from their wall as possible, so as not to tip off their next victim that anything is amiss. Short of demolishing the structure in which she lives, it is impossible to harm a Wall Widow until she reveals herself by taking physical form, and, even then, one must be quick before she melts back into the stone from whence she came.
For comparison/informational purposes, below are some relevant images:
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