Sinful things produced by out-of-head fiends (5)
I believe the answer is:
evils
'out-of-head fiends' is the definition.
I can't tell whether this defines the answer.
'sinful things produced by' is the wordplay.
'sinful' becomes 'evil' (I've seen this before).
'things' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'produced by' says to put letters next to each other.
'evil'+'s'='EVILS'
Can you help me to learn more?
(Other definitions for evils that I've seen before include "Iniquities" , "Lives (anag.)" , "immoral actions" , "Sins and depravities" , "transgressions" .)