Gunther's Kaleidoscopic Strike

When this spell is cast, a thin beam of shimmering, kaleidoscopic light shoots from the wizard's fingertips toward his target. The victim is allowed a saving throw to resist the beam.
This spell has no effect on non-spellcasters, causing them no harm whatsoever. Creatures with innate spell-like abilities are also unaffected. Against wizards and priests, this spell can be devastating. It "short-circuits" the arcane energy stored in a spellcaster's mind, wiping away a number of available spell slots. These slots can only be recovered with time or magical means.
The number of slots drained is equal to the caster's level minus 1d20. Thus, 16th-level wizard drains a maximum of 15 slots, but could drain no slots depending on the die roll. After subtracting the die roll from the caster's level, any result of zero or a negative number indicates that the victim loses no spell slots.
Slots are drained from the wizard beginning with 1st-level spells and working up to higher level slots.

[Tome of Magic]

School: Invocation/Evocation
Level: 8
Rarity: Uncommon

Range: 5 yards/ level
Components: V, S
Duration: Instantaneous
Casting Time: 8 segments
Area of Effect: One creature
Saving Throw: Negates