This is Barbie's sassy Halloween outfit!  Ken and Skipper also had matching ensembles - Skipper's is  Masquerade #1903 (1964 - 1965) .

The costume itself is the easiest piece to find, but it frequently has issues with the ribbons that tie behind the neck.  The hat and mask are hard to find, especially with good, intact elastic.  The pantyhose are prone to runs and snags and are hard to find in great condition.  The shoes are very hard to find with the yellow pompons intact, but they are easy to replace - replacement pompons are easily found at craft stores.  The hardest piece of all to find is the tiny party invitation.

The tulle on the tutu will often be flat, but it is easy to fluff up by separating the layers with your fingers.