Full of mischief (6)
I believe the answer is:
impish
'full of mischief' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for impish that I've seen before include "Mischievous like small devil" , "Mischievous like small fairy" , "Wicked" , "troublesome" , "Naughty" .)