Brat (3)
'brat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for imp that I've seen before include "Small mischievous sprite" , "one likely to cause trouble" , "Elf" , "Naughty demon" , "Evil spirit" .)
(Other definitions for snot that I've seen before include "Contemptible type" , "Dog" , "Mucus" .)