My special ability would be to curse people with severe benzo withdrawals, even if they have never touched benzos or even drugs before. If you piss me off you will be dizzy and seizing and vomiting and shaking and muscle spasming with severe anxiety until you die painfully

probably not really, I would probably choose something more practical, depending on what magic other wizards around me have and how willing they are to help me out using said magic, but it's funny to think about