Plague

Plague was an illusion spell that caused a person or creature to appear as if they were suffering from a horrid, and likely contagious, disease.

Effects
Anyone who saw, smelled, touched or otherwise perceived the individual affected by plague very likely believed them to be afflict by some horrendous illness. As such it was not unusual for them to be shunned, as their existence and proximity posed a perceived threat to anyone nearby. While the illusory effects of the spell were clearly evident to anyone around the affected recipient, they themselves were completely unaware of any changes to their outward appearance.

The effects of this spell lasted for nearly five tendays, continuing longer depending on the skill and experience of the caster. They were not effected by the spell cure disease, but could be dispelled or negated by the caster any time they chose.

Casting
In addition to verbal and somatic components, the casting of this spell required a small amount of soot or fungus that was consumed in the process.

When casting plague, the caster chose a specific disease the effects of the spell mimicked. If they chose an illness with which they were relatively familiar, there was a small chance it could be detected as an illusion upon close examination. If they chose a disease they had never encountered before, or one that was relatively new to Toril, the odds of the illusion's discovery were greatly increased.

Usage
While it may have been tempting for some mages to cast this spell upon a wealthy target and blackmail them to remove its effects, the practice was explicitly illegal in a number of nations in Faerûn.

History
This spell was uniquely found in Selvar's Ineffable Conjurations, Magic, and Phantasms, the personal spellbook of the mage Selvar.