As a master, my, he created havoc! (6)
I believe the answer is:
mayhem
'havoc' is the definition.
('mayhem' can be a synonym of 'havoc')
'as a master my he created' is the wordplay.
I cannot really see how this works, but
'a' is within the answer.
'master' could be 'm' and 'm' is found in the answer.
'he' could be 'em' and 'em' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for mayhem that I've seen before include "Chaos, confusion, destruction" , "Much trouble when" , "Violent or damaging action, a crime" , "Chaos, violent disorder" , "wild state" .)