Imaginary creature -- draw one missing tail (6)
I believe the answer is:
dragon
'imaginary creature' is the definition.
(dragon is a kind of imaginary creature)
'draw one missing tail' is the wordplay.
'draw one' becomes 'dra' (I can't justify this - if you can you should believe this answer much more).
'missing' becomes 'gone' (synonyms).
'tail' means to remove the last letter (I've seen 'tailed' mean this (to tail something can mean to remove its end)).
'gone' with its final letter removed is 'gon'.
'dra'+'gon'='DRAGON'
Can you help me to learn more?
(Other definitions for dragon that I've seen before include "Reptilian monster" , "Continue interminably" , "St George's slew one" , "Fire-breathing creature slain by St George" , "Fire-breathing creature of myth" .)