Who is the mastermind in Scooby Doo night of 100 frights?

The mastermind in Scooby-Doo! Night of 100 Frights is Dr. Phibes. He's a mad scientist who is actually a descendant of the original Dr. Phibes from the classic horror film series.

Dr. Phibes wants to resurrect his dead wife by using the souls of 100 victims to fuel a ritual. He uses the "Night of 100 Frights" theme park to lure in his victims, terrifying them and then using their fear to power his resurrection machine.