When Scooby says, "They drew first blood, not me." This is a direct reference to the 1982 movie, Rambo: First Blood.
The person in a red and white striped sweater wasn't Waldo,it's a dark skinned girl with a hairband
Waldo can be seen as one of the townsfolk working in the caves.
When Scooby, wearing robot armor, jumps on top of Shaggy's shoulders, and his legs extend, the audio sound effect that plays is the same sound used as when Lee Majors as Col. Steve Austin from The Six Million Dollar Man (1974) uses his cyborg abilities.