Shrove Tuesday festival (5,4)
I believe the answer is:
'shrove tuesday festival' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mardi gras that I've seen before include "Shrove Tuesday celebration" , "Carnival (day)" , "Time for carnival" , "Revelry celebrating Shrove Tuesday" , "pre-Lent festival" .)