The Cat Creature was the disguise of Dr. B.B. Bell. Somebody gave Daphne Blake's aunt, Olivia Dervy, a necklace that had the cat creature on it; it would change the lady into the creature to rob jewelry and banks. It turned out to be the lady's doctor, the doctor would reverse the room with a button and the cat creature would be on the other side looking like she transformed into the creature. The doctor would also put large amounts of the jewelry in her room while he was checking her to frame the poor lady. His plan was foiled when Scooby-Doo led him into an elevator, which rose and fell at rapid speed. Once the elevator stopped, the gang was able to unmask the Cat Creature.

Cat Creature (Make a Beeline Away from that Feline)
Dr. Bell