Wreak havoc with a grave consequence (6)
I believe the answer is:
ravage
'wreak havoc' is the definition.
(I've seen this in another clue)
'a grave consequence' is the wordplay.
'a grave' anagrams to 'RAVAGE'.
Though, I am not sure how this is indicated.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for ravage that I've seen before include "Pillage or lay waste" , "Devastate, damage extensively" , "Cause extensive destruction" , "Lay waste, plunder" , "Act like a 6" .)