Sort involved with demo who tells us the end is nigh? (8)
I believe the answer is:
doomster
'who tells us the end is nigh?' is the definition.
(term for someone predicting disaster)
'sort involved with demo' is the wordplay.
'involved with' is an anagram indicator (involved can mean confusing or complex).
'sort' with its letters mixed up with 'demo' gives 'DOOMSTER'.
(Other definitions for doomster that I've seen before include "In Ayr I used to say sentence" , "One predicting disaster" .)