Mythical creature that's still current (4)
I believe the answer is:
yeti
'mythical creature' is the definition.
(yeti is a kind of mythical creature)
'still current' is the wordplay.
'still' becomes 'yet' (yet can mean still or so far).
'current' becomes 'I' (symbol for electric current).
'yet'+'i'='YETI'
'that's' is the link.
(Other definitions for yeti that I've seen before include "He's never had a successful Catcher" , "that is found in Himalayan mythology" , "Bigfoot" , "elusive character" , "mythical monster!" .)