Setter, this setter, to pause - he needs rest following Beelzebub (15)
I believe the answer is:
mephistophelean
'following beelzebub' is the definition.
'setter this setter to pause he needs rest' is the wordplay.
I cannot quite see how this works, but
'setter' could be 'me' (the setter of the clue) and 'me' is found within the answer.
an anagram of 'this' is 'hist' which is within the answer.
'he' is present in the answer.
'rest' could be 'lean' (I've seen this before) and 'lean' is present in the answer.
The remaining letters 'pop' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Another definition for mephistophelean that I've seen is " Diabolical".)