Correct, Priscilla! It was (supposedly) the by-product of a silver mine.
I believe Daphne threw the pipe (lance) into the 10,000 Volt Ghost and Fred attatched the other end of the cables to the Black Knight Ghost.
Okay, Andy - Hmmmm - I think it was to bribe Scooby and Shaggy to follow her into the Spooky Castle on Spooky Island.
Here's another: In "Simply Irresistible" what was the secret ingredient that Amanda uses in her desert to produce the magical fog?
