Quoted from RobT:
He said he got to the "wizard mode" twice in one game. The Stiff-o-Meter is not the wizard mode. Spider Multi-ball is.
The gameplay and goals of Scared Stiff all lead up and through the Stiff-o-Meter, including the awesome show for finishing it. After completing it, the game goals and progress essentially reset as if you completed the game, just like most wizard modes do. Completing the Stiff-o-Meter is the wizard mode of the game by definition.
Spider multiball does not follow the rules and progress of the game. Getting there is almost like completing a video mode 15 times. It's certainly difficult - way more difficult than the Stiff-o-Meter, but it doesn't really follow the main rules, or progress, of the game.