A wizard using this spell, which operates much like a forget spell, can permanently burn from the memory of any one creature all knowledge of either a specific place or person or a time period of up to one year (the spellcaster may choose the desired result). The spell works on any intelligent creature by destroying a portion of its brain, but a victim is entitled to a wisdom saving throw. If successful, the creature suffers only a painful headache, which dissipates in D4 hours but is otherwise harmless. If failed, the victim suffers D6 points of damage from an excruciating headache, leaving him or her with selected gaps in his memory.

Brainkill can affect only the victim's memory and ability to recall factual information. For example, a person thus affected might be completely unable to remember details of a place, the name, appearance, or any traits of a person, or might have a one-year blank in his or her memory. The spell has no effect on a person's learned abilities or skills. For instance, suppose an individual gained a swimming proficiency six months before coming under the influence of this spell. While the victim will no longer recall the swimming lessons, he or she still retains the ability, though it might not become evident until the victim jumps into a large body of water. Aside from relearning it as best as one can, the lost knowledge and memories can never be regained except by a wish.