Chap tempted by Mahdi Army every now and again? (4)
I believe the answer is:
adam
'chap' is the definition.
'mahdi army every now and again?' is the wordplay.
'every now and again?' means one should take alternating letters.
'mahdi'+'army'='mahdiarmy'
The alternating letters of 'mahdiarmy' are 'ADAM'.
'tempted by' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for adam that I've seen before include "Robert ..., ... Clayton" , "First guy" , "Eve's partner" , "First fruit-eater" , "Scottish architect, d.1792" .)