There's little good in lad who is a malign influence? (4)
I believe the answer is:
bogy
'who is a malign influence?' is the definition.
(bogy is an mischievous spirit)
'there's little good in lad' is the wordplay.
I cannot quite understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is found within the answer.
'lad' could be 'boy' (I've seen this before) and 'boy' is present in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
(Other definitions for bogy that I've seen before include "Evil mischievous spirit" , "thing feared" .)