Backlash

Backlash was a single target spell that affected spellcasters only, such as wizards and clerics. If cast upon non-spellcasting classes, the spell would be entirely nullified.

Effects
Upon casting the spell, a barely detectable dweomer would be placed upon the target. However, there was not immediate effect. Instead, the dweomer would last until the target cast a spell. Backlash couldn't be removed by standard measures, such as a dispel magic spell.

When the dweomer magically detected a spell being cast by the target, which failed, it is reversed on the target themselves. It also ignored any of the target's saving throw or immunities to the effect of the reversed spell.

Interestingly, the spell could be cast several times on a target. This wouldn't, however, cause a single cast spell to backlash several times. Instead, it would form an order where the earliest spell backlashes first, followed by the rest.

History
This spell was used amongst the drow, and it was said that some accomplished drow wizards had formed a 5th level version of the same spell. For this level of the spell, the backlash could stack up to 5 times, but as little as 2. Thus, in the case of 2 backlashes, if the target of the spell cast acid bolt, nothing would occur. However, if the target then cast magic missle, both an acid bolt and magic missile would affect the caster. This could potentially have resulted in a barrage of offensive spells being fired back at the caster.

Appearances

 * Computer games:
 *  Menzoberranzan