Intelligence Reduction – The ability to reduce the intelligence of others. Intelligence Reduction is also known as Intelligence Decline and Kogata no Smarts.
The Intelligence Devourer literally devours the intelligence of the victim (D&D 4th Edition – Monster Manual 3).
Doctor Doom (Marvel) has his intelligence reduced by Bruce Banner in Incredible Hulks #606.
Jack Hawksmoor has his intelligence reduced by The Authority V1 #27.