Elminster's Effect Twister

When cast, the spell imposes a state of diminished effectiveness on all damage rolls, skill checks, spells and spell-like powers used by the targeted creature for the duration. The spell causes all the spells and spell-like powers of the victim to function at the nadir of their effectiveness. Any damage caused by offensive magics will be the minimum possible, saving throws versus the victim’s spells are at +4, and any ongoing spells are altered (for example, a creature previously charmed by the victim would receive another saving throw). Any ongoing spells or enhancements active on the target are likewise modified to minimal efficacy. Unwilling targets may save versus the caster's DC to avoid the effects of this spell. A target may choose to willing fail a saving throw against the spell. - (Thus an affected target casting a spell doing 3d6 damage would do just 3 points of damage)

The reverse of this spell empowers the target creature to use its spells or spell-like abilities at their maximum effectiveness. - (Thus an affected target casting a spell doing 3d6 damage would do 18 points of damage, and any spell variables would be at their maximum efficacy.)

In addition to verbal and somatic components, this spell requires a material component of a glass prism, which is shattered as the spell is cast.