Nilbogs were goblins possessed by trickster spirits, the result of a condition known as nilbogism. A possessed goblin was a prankster and impish creature, capable of affecting the behavior of those surrounding it and of sowing chaos among its allies and enemies alike.
When struck by any harmful attack, a nilbog would instead heal. Moreover, any attempt to harm a nilbog risked the attacker falling victim to nilbogism, becoming compelled to praise the nilbog instead of attacking it. Adventurers might feel compelled to hand over all their possessions to a nilbog.
A nilbog would, however, refrain from using its powers if it received constant praise and respect from other members of the group.
Nilbogs were more likely to appear in locations where goblins were particularly mistreated or, in rare cases, where heavy use of magic distorted space and time. The very possibility that a nilbog might appear struck terror in hobgoblin and bugbear commanders, who were well aware that nilbogs were extremely difficult to harm, and even so, killing one merely caused the spirit to flee and possess another goblin.
For that reason, most goblinoid armies included a position of "jester", usually assigned to the most obnoxious goblin. The jester was offered freedom to behave however it wished and to go anywhere it wanted. For that reason, the position of jester was highly sought after by goblins.
Some magic items existed that were either inspired by the nilbogs' inversion of reality or actually required them for their creation. Magic arrows known as nilbog arrows created an illusion of damage when hitting a target, but instead had curative powers. Magic hourglasses known as Auquhol's hourglasses used powdered nilbog bones as their sands.
The goblins believed that the nilbog spirits were fragments of a trickster deity in the goblin pantheon. This god remained nameless so that Maglubiyet did not find and destroy it as he had done with the other goblin deities.
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