This spell had three variants, one of which had to be chosen at the time of casting. The first variant prevented magical darkness from enveloping the caster—all manner of darkness spells targeting the caster of dark mirror, or in the vicinity, were countered. The second variant reflected all darkness spells back upon their caster. If the target of the reflection resisted his or her own spell, then it fizzled. The caster of dark mirror could choose to reflect magical darkness spells back to the location of the attacker, rather that at the attacker's person, in which case no resistance was possible, but the attacker could choose to leave the darkened area. The third variant allowed the caster to be unimpaired by magical darkness, seeing as they normally would, out to a distance of 10 ft (3 m) per level of the caster.
The first two variants of dark mirror had a duration of at least three minutes—longer for more experienced wizards—and would counter or reflect all magical darkness spells until the spell expired. The range for reflection was 10 yd (9.1 m) per level of the caster. The third variant allowed the caster to see through magical darkness for a minimum of 30 minutes (again, longer for more experienced casters).
In addition to verbal and somatic components, this spell required a small mirror and a candle (lit or not).
This spell was created by a wizard named Jume from Baldur's Gate several centuries before the Time of Troubles. She recorded it in her book, the Arcanabula of Jume, which occasionally teleported to a random location in the Realms. Over the centuries, its contents gradually became more familiar to practitioners of the The Art.