Achieves destruction of satanist without leader (7)
I believe the answer is:
attains
'achieves' is the definition.
('attain' can be a synonym of 'achieve')
'destruction of satanist without leader' is the wordplay.
'destruction of' indicates an anagram.
'without leader' means to remove the first letter.
'satanist' with its first letter taken away is 'atanist'.
'atanist' is an anagram of 'ATTAINS'.
(Other definitions for attains that I've seen before include "Reaches, succeeds in getting" , "effects" , "Realises" , "Reaches, accomplishes" , "Achieves" .)