One of the cool things about Peanuts was that Snoopy was accepted as one of the gang, instead of being Charlie Brown's dog. This allowed for creator Charles Schulz to put Snoopy in some very unusual situations.
1981's "It's Magic, Charlie Brown" is just one of those situations. Rebuked by Charlie for doing little more than eating & sleeping, Snoopy is sent to the library, as Charlie loans him his library card. Snoopy gets a book on magic, and, of course, chaos follows.
Unsurprisingly, a familiar trope to fans of the strip appears, as Snoopy quiets a heckler not once, but twice, early in his act as "The Great Houdini".
Actress Sydney Penny, who voiced Lucy this time around, would go on to a modest film & television career, and if I'm not mistaken, is the only one in this cast who did so.