Stultify

stul·ti·fy /ˈstʌltəˌfaɪ/ Pronunciation Key - Show Spelled Pronunciation[stuhl-tuh-fahy]
–verb (used with object), -fied, -fy·ing

1.	to make, or cause to appear, foolish or ridiculous.

2.	to render absurdly or wholly futile or ineffectual, esp. by degrading or frustrating means: Menial work can stultify the mind.

3.	Law. to allege or prove (oneself or another) to be of unsound mind.

This should be a Harry Potter spell EXPECTOPATRONUM! IMPEDIMENTA! STULTIFY!