Mum goes to town with him (5)
I believe the answer is:
mario
'him' is the definition.
'mum goes to town' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'goes to' is a charade indicator (letters next to each other).
'town' becomes 'rio' (I am not sure about this - if you are sure you should believe this answer much more).
'ma'+'rio'='MARIO'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for mario that I've seen before include "Lanza" , "-- Puzo, author of The Godfather" .)