"Mash taro!', urges stand-in (9)
I believe the answer is:
surrogate
'stand-in' is the definition.
(I know that stand-in can be written as surrogate)
'mash taro' urges' is the wordplay.
'mash' is an anagram indicator (I've seen this in other clues).
'taro'+'urges'='tarourges'
'tarourges' is an anagram of 'SURROGATE'.
(Other definitions for surrogate that I've seen before include "Deputising substitute" , "Argues about rot with substitute or deputy" , "stand-in" , "One standing in" , "(A) substitute in office" .)