The Shadow Stalker

The Shadow Stalker is a figure whispered about in fearful tones, a spectral predator of The Veil lurking in the darkest shadows of the world. Its form is a vaguely humanoid silhouette, compsed of swirling pitch-black mist, forever shifting and twisting like smoke caught in an unseen wind. Unline other creatures of darkness, the Shadow Stalker lacks any solid structure save for a single feature: a long, slick tongue that snakes from its shadowy mouth, as areal and solid as any living being.
The Shadow Stalker's true power lies in its ability to render others helpless, its tendrils of shadow silently slipping through the air to envelop its chosen prey. Once its tendrils have coiled around its victim, the creature uses its insidious tongue to invade their mind and voice, bending them to its will like a ventriloquist manipulates a puppet. In this way, it doesn't need to speak; it communicates through the mouths of those it ensnares, forcing them to reveal hidden truths, confess sins or speak words that were never their own. 
As it tightens its grip, the Stalker's influence grows, sapping the victim's strength and draining them of will. Those caught in its grasp describe feeling a creeping numbness, as if their very essence is being swallowed by the shadows. Rumour has it that if the Shadow Stalker remains latched onto its prey for too long, they lose their voice forever, left mute and haunted, with only faint memories of the darkness that overtook them. 
Legends say that they Shadow Stalker was once a mortal creature, perhaps even a sentient creature at one point, cursed to wander in darkness, doomed to siphon the voices of others to replace its own. Now it haunts the edges of society, seeking out those whose minds are weakened by fear or guilt. Its presence is marked by an unnatural chill, a creeping sense of dread, and the unsettling feeling of being watched by unseen eyes. Those who survive its grasp are unable to speak of it again, as if even uttering its name might summon it back from the shadows.