Angel perhaps trapping Devil, which might provide relief (13)
I believe the answer is:
backscratcher
'angel perhaps trapping devil which might provide relief' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'angel perhaps trapping devil' is the wordplay.
'angel perhaps' becomes 'backer' (I can't explain this - if you can you should believe this answer much more).
'trapping' means one lot of letters goes inside another.
'devil' becomes 'scratch'.
'backer' going around 'scratch' is 'BACKSCRATCHER'.
Can you help me to learn more?
(Other definitions for backscratcher that I've seen before include "Long-handled itch-remover" , "one engaged in dubious exchanges" , "Long-handled itch remover?" .)