Trush

Trush is a shadow demon and patron of the goblin warlock Bol'bara.

Background
In 835 PD during the War of Ash and Light, Bol'bara, a goblin elder of Urzin, journeyed out of the village within Brokenveil Marsh to a ritual stone in order to gather spell components and commune with Trush, her patron. However, Bol'bara was captured by a garrison of Righteous Brand soldiers lead by the Imperial Inquisitor Parson Pellinost, and taken to the Imperial outpost Fort Venture for questioning and torture. With her rite interrupted, Bol'bara became host to Trush.

Unwelcome Spirits
At Fort Venture, Pellinost, a cultist of Vesh the Bloody Siren tortured Bol'bara by killing her each day then resurrecting her with the spell Revivify. On the third day of this torture, Bol'bara became fully possessed by Trush. With this power granted, she used her Zone of Calamity to cause Pellinost's guard to attack and kill him. She escaped and wreaked havoc across Fort Venture, killing everyone at the fort save for another prisoner, Alonne Frith.

After escaping the fort, Bol'bara led a path of destruction back through the Brokenveil Marsh towards Urzin. Trush, being a demon, desired chaos and to use Bol'bara as its host to achieve that end. When found by the adventuring party that Buhfall II hired to recover her, they could with great difficulty attempt to reason with Trush to relinquish Bol'bara. Instead they could also knock the goblin unconscious and quickly revived her, after which her possession would end.

Relationships
Trush acts as a warlock patron to Bol'bara granting her a measure of power. However once Trush possessed Bol'bara, it was unlikely to relinquish her and would continue to use her for its own chaotic ends unless stopped by an outside force.

Abilities
As a shadow demon, Trush likely has the following abilities:
 * Damage Resistances: Acid, cold, fire, necrotic, thunder; nonmagical bludgeoning, piercing, and slashing
 * Damage Immunities: Lightning, cold, poison
 * Damage Vulnerabilities: Radiant
 * Incorporeal Movement: Trush can move through creatures and objects, taking force damage if it ends its turn in an object.
 * Light Sensitivity: While in bright light, Trush has disadvantage on attack rolls and perception checks that rely on sight.
 * Shadow Stealth: Trush can hide as a bonus action in dim light or darkness.
 * Claws: deals psychic damage on a hit. Deals additional damage if the attack has advantage.

As Trush granted this ability to Bol'bara while possessing her, it may also have the following Legendary Action:
 * Zone of Calamity: Creatures that start their turn within 15 feet of Trush must make a Wisdom save or be effected as though by the Confusion spell. The zone lasts for one minute and requires Trush's concentration.