Legendary Himalayan, still impressive to begin with (4)
I believe the answer is:
yeti
'legendary himalayan' is the definition.
(I've seen this in another clue)
'still impressive to begin with' is the wordplay.
'still' becomes 'yet' (yet can mean still or so far).
'to begin with' suggests taking the first letters.
The first letter of 'impressive' is 'i'.
'yet'+'i'='YETI'
(Other definitions for yeti that I've seen before include "Himalayan enigma" , "that you might find in mountains" , "seeks him in the Himalayas" , "elusive character" , "Tibetan wild man" .)