When Shaggy and Crystal are viewed from a distance walking together and talking, you can hear him telling her the story about his first encounter with the Witch's Ghost from Scooby-Doo and the Witch's Ghost (1999).
This is Mary Kay Bergman's last movie as Daphne Blake. She died by suicide in 1999, and this 2000 film is dedicated in her memory. Her friend, Grey DeLisle, would provide the voice of Daphne Blake in all future Scooby-Doo movies starting with Scooby-Doo and the Cyber Chase (2001), which was released the following year.
This is the second time Mark Hamill (Steve) voiced a character in the direct-to-video series of Scooby-Doo films. He also voiced Snakebite Scruggs in Scooby-Doo on Zombie Island (1998).
At the movie's beginning, the loud signal heard through the radio monitors is referencing the "WOW" signal. Which was a strong narrowband radio signal heard in 1977 and is the strongest candidate for an alien radio transmission ever detected.
In this film, and others from the late 1990s and early 2000s, the gang wears modern clothing and drives an updated Mystery Machine. During Shaggy's dream sequence, there is a scene where the gang is in their original Scooby Doo, Where Are You! (1969) costumes, and Shaggy drives away in the original Mystery Machine.