Mild reprimand: who'd be a mummy! (3)
I believe the answer is:
tut
This clue might be a double definition.
'mild reprimand who'd' is the first definition.
The definition suggests a singular noun which matches the answer.
'a mummy' is the second definition.
Both the answer and definition are singular nouns.
Maybe you can see an association between them that I can't see?
'be' acts as a link.
Can you help me to learn more?
(Other definitions for tut that I've seen before include "Exclamation of disapproval or annoyance" , "I disapprove" , "Expression of disapproval, usually doubled" , "That's bad!" , "Disapproving noise" .)