This requires the Hillbilly, Knight and Time Traveler. When at the carnival, collect the Wrench, Sledgehammer and Barbell. While holding these items, stand on the scales. Note: This must be done before solving the scales puzzle. The total weight of all objects and characters used to reach 666lbs are as follows.
If you take a hot dog from the vending machine at the beginning of the game into the Zoo level, you can take it to the Crystal Cave Monster and lure it to the bridge so it dies. That way you don't need to do the whole Zoo level or get the huntress away from the hot dog vending machine.