Briefly stop seeing grotesque creature (6)
I believe the answer is:
goblin
'grotesque creature' is the definition.
(I've seen this before)
'briefly stop seeing' is the wordplay.
'briefly' means to remove the last letter.
'stop seeing' becomes 'goblind' (to go blind is to stop seeing).
'goblind' with its final letter taken off is 'GOBLIN'.
(Other definitions for goblin that I've seen before include "Mischievous ugly creature of folklore" , "Malevolent gnome" , "Malevolent imp" , "Mischievous dwarf" , "mischievous spirit" .)