A film star appears when this creature visits Massachusetts Street (3)
I believe the answer is:
ewe
'this creature visits massachusetts street' is the definition.
'ewe' can be an answer for 'creature' (I've seen this before). I am unsure of the remainder of the definition.
'a film star appears when' is the wordplay.
I cannot really see how this works, but
'film' could be 'w' (W, film about George W Bush) and 'w' is found within the answer.
'when' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
A single letter 'e' remains which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
(Other definitions for ewe that I've seen before include "Ruminant" , "Scottish loch" , "Farm animal" , "Female animal" , "Lamb supplier" .)