Demoniac
WordNet
adjective
(1) Resembling or suggesting possession by a demon
"Demoniac energy"
"A demoniacal fit"
(2) In a murderous frenzy as if possessed by a demon
"The soldier was completely amuck"
"Berserk with grief"
"A berserk worker smashing windows"
noun
(3) Someone who acts as if possessed by a demon