Completely using different lethal method (3,3,3)
I believe the answer is:
all the way
'completely' is the definition.
(both can mean to the fullest extent)
'different lethal method' is the wordplay.
'different' indicates anagramming the letters.
'method' becomes 'way' (way of doing something).
'lethal' anagrammed gives 'allthe'.
'allthe'+'way'='ALL THE WAY'
'using' acts as a link.
(Other definitions for all the way that I've seen before include "without limit" , "Without reservation" , "to the end" , "Sinatra sang this" , "Completely" .)