Stated reason French writer briefly creates heraldic beast (6)
I believe the answer is:
wyvern
'heraldic beast' is the definition.
(I've seen this before)
'stated reason french writer briefly' is the wordplay.
'stated reason' becomes 'wy' (I can't explain this - if you can you should believe this answer much more).
'french writer' becomes 'verne' (author Jules Verne).
'briefly' means to remove the last letter.
'verne' with its last letter taken away is 'vern'.
'wy'+'vern'='WYVERN'
'creates' is the link.
Can you help me to learn more?
(Other definitions for wyvern that I've seen before include "Heraldic dragon with two legs and two wings" , "Heraldic form of dragon" , "In heraldry, a dragon with wings, two legs and a barbed tail" , "1950s Vauxhall model" , "Fabulous creature" .)