Brood Gibberling

The shrieking gibberlings that plague the world are now thought to be the warped remains of ordinary humanoids, made by brood gibberlings. These parents are pale, misshapen humanoids with pitlike, drooling mouths, filthy black manes and eyes full of sly malice. Worst of all, their skin crawls: small parasites called gibberslugs scurry beneath it, leaving trails of slowly sinking lumps behind them. Seen in the open, a gibberslug looks like a swollen leech the throbbing pink of a newborn mouse, with a mouth built for piercing hide.

A brood gibberling's bite has a 50% chance of slipping a slug into the wound. Every 4 rounds it may also spit one at a melee opponent (dagger range), on top of its normal action and before other actions resolve. Anyone struck by either must save vs. death or fail to dislodge the slug before it burrows in.

Fire on the entry wound within one round kills the slug, costing the host 1d4 damage. Eating darkscape, a rare mushroom that grows only in lands warped by the Farther Dark, also kills a burrowing slug outright. Otherwise the host takes 1d4 damage per round as it tunnels toward the brain, which it reaches in 1d6+5 rounds. It then fuses to the brain stem and the host falls into an unwakeable sleep full of hideous nightmares; from this point only a wish can save him. Over 1d20+4 hours the slug eats brain and body from within, and a full-grown gibberling climbs out of the empty skin. It faintly resembles the victim, remembers nothing, and either attacks the closest creature not of its kind or, if bright light falls on it, flees to find its own.

Brood gibberlings come from a realm that may lie outside the known planes, slipping through carelessly opened gates. Most cannot survive far from the corruption that spreads for miles around such gates, though their offspring roam freely. Their burrows are littered with ragged husks from past births. Each brood gibberling mentally commands every gibberling it has made, so each heads a clan; clans may ally or fight at their masters' whim, and brood gibberlings try to win other clans' gibberlings over to their own.

What these beings look like in their native realm is anyone's guess, and probably nothing like their form here.