Standing as tall as a man, the shrieker is a pale, mindless fungus that thrives in the lightless reaches of the Underdark or the dampest corners of ancient ruins. Though it lacks eyes, it is preternaturally sensitive to movement and light, vibrating with a low, imperceptible hum until disturbed. These fungal growths are often cultivated by subterranean denizens—such as drow, duergar, or troglodytes—to serve as living burglar alarms. When a stray torchbeam or an intruder’s footfall agitates the creature, it erupts in a piercing, discordant wail that can be heard through hundreds of feet of solid rock, signaling an immediate end to stealth and a dinner bell for nearby predators. Adventurers often mistake a dormant shrieker for a common violet fungus or a harmless oversized mushroom until its deafening cacophony begins. In some forgotten vaults, these fungi have been magically crossbred to exhale hallucinogenic spores alongside their scream, disorienting thieves while the complex’s guardians close in. A party might find themselves in a cavern where the walls are thick with these pale stalks, realizing too late that their only path forward requires absolute darkness and the stillness of the grave, lest they wake a chorus that will alert every horror in the deep.