Purple People Eater (1988)

Continuity mistake: When the condo manager shows up at Billy's house to take Purple, and chases him round the garage, some stuff, including a white plastic basket, falls off a shelf twice; first in the wide shot, then again in a closeup of Purple's feet.

Grandpa: Look! Purple may be a little strange.
Mrs. Orfus: Yes!
Grandpa: But that's because he is a brilliant musician!
Mrs. Orfus: No! No! Purple is an alien!