Circus performer got up as a pixie (4)
I believe the answer is:
flea
'circus performer' is the definition.
(as in a flea circus)
'up as a pixie' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'as' becomes 'a' (I can't explain this - if you can you should believe this answer much more).
'a pixie' becomes 'elf' (synonyms).
'a'+'elf'='aelf'
'aelf' back-to-front is 'FLEA'.
'got' is the link.
Can you help me to learn more?
(Other definitions for flea that I've seen before include "Tiny circus performer?" , "Insect (which you don't want in your ear!)" , "Small jumper in small circus" , "In one's ear, it's a stinging rebuke" , "Bug" .)