Fabulous creature still on island (4)
I believe the answer is:
yeti
'fabulous creature' is the definition.
(I've seen this in another clue)
'still on island' is the wordplay.
'still' becomes 'yet' (yet can mean still or so far).
'on' says to put letters next to each other.
'island' becomes 'i' (geographical abbreviation).
'yet'+'i'='YETI'
(Other definitions for yeti that I've seen before include "A sort not reliably recorded" , "creature awaiting discovery?" , "that you might find in mountains" , "Hairy recluse" , "Himalayan monster?" .)