Mythical mountain monster (4)
I believe the answer is:
yeti
'mythical mountain monster' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yeti that I've seen before include "Legendary Himalayan creature" , "creature never actually seen" , "Himalayan mystery" , "Himalayan legend" , "An abominable animal!" .)