Revealing mistake: Just after the pterodactyl ghost has been "tied up", it flies off. When Shaggy and Scooby are looking at the ropes, Fred and Daphne duck at the same time. Obviously it was meant to look like they are ducking when the pterodactyl's wings flap, but the pterodactyl has already flown off. (00:09:00)
Revealing mistake: When Fred rushes in to fight the Black Knight Ghost in Mr. Wickles' castle, he is hit in the face several times with the back of his shield. As he falls, you can see the pad on the back of the shield to protect his face. (It is not noticeable when he first runs in.) (00:23:20)
Revealing mistake: When Shaggy and Scooby fly off the cliff into the Mystery Machine you can see Daphne and Velma's hair hanging unnaturally towards the left, indicating that the set is on its side so Shaggy and Scooby look like they fly into the van. (00:55:45)
Revealing mistake: When Daphne is attacking the 10,000 Volt Ghost, she falls on the ground besides Fred but it's not on soil. It looks like a mattress. (01:08:10)
Revealing mistake: When Velma is running from the two one eyed skeletons she goes into what looks like a warehouse and the floor is all wet and in some places there are puddles. When the skeletons come they step into a puddle but the water doesn't even splash or ripple. (01:11:20)
Answer: Yes! There was a real Heather Jasper Howe! Like the fake Heather Jasper Howe's True Identity is Jonathan Jacobo! He was arrested with Ned.