He plays tricks with a letter copier (5)
I believe the answer is:
japer
'he plays tricks' is the definition.
The definition suggests a singular noun which matches the answer.
'with a letter copier' is the wordplay.
'with' means one lot of letters go next to another.
'a letter' becomes 'j' ().
'copier' becomes 'aper' (ape can mean to copy or imitate).
'j' put next to 'aper' is 'JAPER'.
Can you help me to learn more?
(Other definitions for japer that I've seen before include "trickster" , "joker" , "One jokes" .)