Perverted anti-mass in devil worship (8)
I believe the answer is:
satanism
'devil worship' is the definition.
(I've seen this before)
'perverted anti-mass' is the wordplay.
'perverted' indicates anagramming the letters.
'anti'+'mass'='antimass'
'antimass' is an anagram of 'SATANISM'.
'in' is the link.
(Other definitions for satanism that I've seen before include "Devil-worship" , "Worship of the devil using mantissa" , "Evil praying" , "Belief in and reverence for the devil" .)