Popular remix of 'So Vain' becomes offensive (8)
I believe the answer is:
invasion
'offensive' is the definition.
(thesaurus)
'popular remix of so vain' is the wordplay.
'popular' becomes 'in'.
'remix of' is an anagram indicator.
'so'+'vain'='sovain'
'sovain' is an anagram of 'vasion'.
'in'+'vasion'='INVASION'
'becomes' is the link.
(Other definitions for invasion that I've seen before include "Encroachment, intrusion" , "Occupation" , "Incursive attack" , "Offensive" , "Incursion, entry for conquest" .)