This monster looks and acts exactly like a goblin, even speaking the same language. The one difference between a goblin and nilbog, however, is a very important one. Goblins infected with nilbogism are surrounded by a weakness in the eldritch fabric that separates magic and magical energy from reality. Whereas in most cases such weaknesses result in null magic zones, when contained within the nilbog’s life essence these tears in reality have a completely different effect.

Results of being in the presence of a nilbog are chaotic and unpredictable, but always totally contrary to what the adventurer would normally desire.

A thief sneaking into a nilbog lair might start singing at the top of her voice, a magic user might discard a travelling spell book or favourite magic wand, or a party might feel compelled to fill an empty treasure chest in the nilbog lair with their most valuable items. Persons encountering a nilbog have no choice to avoid these reversed sensibilities; no saving throw is allowed. A wish spell or similarly powerful magic should provide a short-lived and limited area immunity to the effects of nilbogism.

Nilbogism also asserts its effect in combat. Striking a nilbog or casting damaging spells at it actually adds hp to the creature equal to the amount of damage that would have been inflicted normally. The only way to damage a nilbog appears to be curative magic, such as casting a cure light wounds spell on it. This harms the creature rather than healing it. (Some adventurers report success with force-feeding the nilbog healing potions.)

Because nilbogs look exactly like goblins, the only way to tell one from the other is to approach it. Of course, since approaching a nilbog subjects one to the effects of nilbogism this is a risky method, at best.

Even more rarely, nilbogism occurs in other creatures, the most ludicrous of which is the llort—a troll-like creature that if cured of damage, begins to degenerate at 3hp per round until dead.