Monstrous creature depicted by that fellow in church, an artist (7)
I believe the answer is:
chimera
'monstrous creature' is the definition.
(mythical creature)
'that fellow in church an artist' is the wordplay.
'that fellow' becomes 'him' (**).
'in' is an insertion indicator.
'church' becomes 'ce' (abbreviation for Church of England).
'an artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'him' inserted within 'ce' is 'chime'.
'chime'+'ra'='CHIMERA'
'depicted by' acts as a link.
(Other definitions for chimera that I've seen before include "fake image" , "Illusory aim; monster" , "Illusion" , "Creature such as a gryphon" , "Mythological animal; something illusory" .)