Feedback Shock (3.5e Spell)
From D&D Wiki
|Range:||50ft +10ft/two levels|
|Target, Effect, or Area:||target spellcaster|
|Saving Throw:||Fortitude negates|
This Spell may be cast at any time. When any creature or character casts a spell or spell-like ability, the Caster of this spell may use it on that creature/character. If the subject fails their Fortitude save they take 1d12/3 caster levels shock damage (max 3d12) and must make a concentration check. If they fail the Concentration check the spell fails and the slot is lost for the day. If they succeed the save they complete the spell.