From the caster's hand, a shimmering, color less ray stabs out to the target; if the target is within range and not completely enclosed by solid or liquid material, the ray strikes unerringly (no attack roll required), dodging around obstacles, other creatures, etc. When struck, the target creature must make a successful saving throw vs. spell (spellcasters at a -1 penalty) or forget one item of magical knowledge at random. If the target creature has one or more spells memorized, one spell will be forgotten, harmlessly lost, as if an attempt to cast it had failed. If the creature is not a spell-caster, or has no spells memorized at the time, any of the following may be forgotten: the command word of a magical item; the name of a spellcaster known to the creature; a legend, rumor, or piece of news involving magic use; the name or configuration of a magical symbol, glyph, or rune; or some other fact of the same sort. Only a heal, restoration, or wish spell restores the lost knowledge.
The target creature must have been seen, however briefly, by the wizard in the turn prior to the casting of the ray of oblivion. The ray will seek out a target that is within range but obscured by cover, invisible, blinking, or even ethereal at the moment of the completion of an enchanter or mentalist; otherwise, very rare. Originally from the Forgotten Realms setting. (Updated from Dragon Magazine.)