Biblical baddie, not half bizarre once (5)
I believe the answer is:
antic
'bizarre once' is the definition.
(historical term for 'bizarre')
'biblical baddie not half' is the wordplay.
'biblical baddie' becomes 'antichrist'.
'not half' suggests halving the letters.
'antichrist' cut in half is 'ANTIC'.
(Other definitions for antic that I've seen before include "seen to be bizarre, at one time" , "Ludicrous act done for fun" , "Frolic" , "Eccentric once" , "Playful or mischievous act" .)