Take complaint from mostly despicable character (3)
I believe the answer is:
cur
'despicable character' is the definition.
(I've seen this in another clue)
'take complaint from mostly' is the wordplay.
'take complaint' becomes 'cu' (I can't justify this - if you can you should believe this answer much more).
'from' becomes 'fr' (abbreviation).
'mostly' means to remove the first letter.
'fr' with its first letter removed is 'r'.
'cu'+'r'='CUR'
Can you help me to learn more?
(Other definitions for cur that I've seen before include "Mongrel; rascal" , "Non-pedigree dog" , "Lowly dog" , "A worthless dog or contemptible person" , "Wretch" .)