Fantastic Mere Man is coming! (8)
I believe the answer is:
emergent
'is coming' is the definition.
(coming can mean emerging or arriving)
'fantastic mere man' is the wordplay.
'fantastic' indicates anagramming the letters.
'man' becomes 'gent' (gent is a kind of man).
'mere' with letters rearranged gives 'emer'.
'emer'+'gent'='EMERGENT'
(Other definitions for emergent that I've seen before include "In the process of coming into prominence" , "Rising" , "Coming into existence" , "Breaking" , "making an appearance" .)