Alien of the week

Alien of the week was a type of literary device in which a serialized fictional story featured a weird alien species in one episode.

In 2381, during the Crisis Point II: Paradoxus holoprogram, Knicknac was dismissed as an alien of the week. (LD: "Crisis Point 2: Paradoxus")

This is a popular motif in science fiction television programs, including Star Trek.