Mythical monster found in tundra - go north! (6)
I believe the answer is:
dragon
'mythical monster' is the definition.
(I know that dragon is a type of mythical monster)
'in tundra go north' is the wordplay.
'in' indicates the answer is hidden within the clue.
'DRAGON' is hidden in the letters of 'tundra go north'.
'found' acts as a link.
(Other definitions for dragon that I've seen before include "battleaxe" , "Fire-breathing beast" , "Fiery monster" , "Racing yacht" , "Fire-breathing creature slain by St George" .)