Some proclaim it a terrible ape (7)
I believe the answer is:
imitate
'ape' is the definition.
(I know that ape is a more specific form of mock)
'some proclaim it a terrible' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'IMITATE' is hidden within 'proclaim it a terrible'.
(Other definitions for imitate that I've seen before include "I ate Tim! (anag.)" , "Mock" , "Take as a model" , "Reproduce" , "Copy, simulate" .)