Odd parts forgotten, is mantra one for evil spirit? (5)
I believe the answer is:
satan
'for evil spirit?' is the definition.
(thesaurus)
'odd parts forgotten is mantra one' is the wordplay.
'odd parts forgotten' means one should take alternating letters (letters in odd-numbered positions removed).
'is'+'mantra'+'one'='ismantraone'
The alternating letters of 'ismantraone' are 'SATAN'.
(Other definitions for satan that I've seen before include "Old Nick, Lucifer or Beelzebub" , "The devil, Beelzebub" , "Fallen archangel" , "Apollyon" , "Diabolical figure" .)