Unconventional fellow to perform an act of exorcism? (4,6)
I believe the answer is:
free spirit
'unconventional fellow' is the definition.
(a free spirit is an unconventional person)
I don't understand how the rest of the clue works.
(Other definitions for free spirit that I've seen before include "one not afraid to flout convention" , "What Prospero promises to do" , "Individualist" , "supplying endless drinks on the house" , "Uninhibited person" .)