Mischief-maker, one to get freedom from punishment (8)
I believe the answer is:
impunity
'freedom from punishment' is the definition.
(I've seen this before)
'mischief-maker one' is the wordplay.
'mischief maker' becomes 'imp' (I've seen this in other clues).
'one' becomes 'unity' ('unity' can be a synonym of 'one').
'imp'+'unity'='IMPUNITY'
'to get' acts as a link.
(Other definitions for impunity that I've seen before include "Complete protection from unpleasant consequences" , "Freedom from punishment" , "Protection from blame" , "Rascal, by agreement, gets exemption" , "impossibility of punishment" .)