Puzzling creature getting sum wrong (8)
I believe the answer is:
bemusing
'puzzling' is the definition.
(I've seen this before)
'creature getting sum wrong' is the wordplay.
'creature' becomes 'being' (I am not sure about this - if you are sure you should believe this answer much more).
'getting' indicates putting letters inside.
'wrong' is an anagram indicator.
'sum' with letters rearranged gives 'mus'.
'being' enclosing 'mus' is 'BEMUSING'.
Can you help me to learn more?
(Other definitions for bemusing that I've seen before include "Like a puzzle" , "puzzling" .)