Fairy bringing up vessel before king (4)
I believe the answer is:
puck
'fairy' is the definition.
(puck is a kind of fairy)
'up vessel before king' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'vessel' becomes 'cup' (I've seen this in other clues).
'before' is a charade indicator (letters next to each other).
'king' becomes 'k' (abbreviation for king in chess).
'cup' back-to-front is 'puc'.
'puc'+'k'='PUCK'
'bringing' is the link.
(Other definitions for puck that I've seen before include "Fairy - ice hockey "ball"" , "gets knocked about with sticks" , "one spun across the ice" , "One icily struck by player" , "One of 5 [FAIRIES]" .)