Behaves mischievously and cat-puss, tailless, suffers (4,2)
I believe the answer is:
acts up
'behaves mischievously' is the definition.
I can't tell whether this definition defines the answer.
'cat-puss tailless suffers' is the wordplay.
'tailless' means to remove the last letter (the tail of the word is removed).
'suffers' indicates anagramming the letters.
'cat'+'puss'='catpuss'
'catpuss' with its last letter taken away is 'catpus'.
'catpus' with letters rearranged gives 'ACTS UP'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for acts up that I've seen before include "Malfunctions" , "Carries on" , "Behaves in a troublesome way" , "Behaves badly (colloq.)" , "Causes trouble or misbehaves" .)