Monster disguises are extremely powerful in the Scooby-Doo universe. They are far more likely to be taken at face value as real monsters than in our world (which may be a villainous counterpart to the disguise tricks of the heroes). In addition, they seem to have powerful properties of their own that may be the result of toon physics.
Full-head masks with realistic jaw movement and facial expressions have been around for some time (usually these masks are made out of silicone rubber, or foam latex that has been applied to the wearer using adhesives like spirit gum), while the masks in the Scooby-Doo universe can be more capable of the following...
Magical costume properties
- Monster masks allow people to have huge mouths, sometimes with weird properties such as the smaller faces inside the Ghost from A Bicycle Built for Boo! or the prehensile tongue of Dr. Croaker.
- Masks can make people's eyes glow or appear a different color, without obscuring their sight. Sometimes if the eyes on a mask are sculpted or painted onto the rubber of the mask (the real eyeholes would be slits hidden either under the mask eyes, or in the nose or mouth holes), the fake eyes can blink and be fully expressive.
- Ghost costumes can make people semi-transparent, as in Guess Who's Knott Coming to Dinner.
- Costumes seem to give their wearers extraordinary strength and fighting skill. An out-of-shape bank president can take out a bank guard if he's in a Creeper outfit.
- One mask can be worn over another, with no problems of volume (such as when the Ape Man disguised himself as Scooby-Doo, wearing a rubber Scooby mask over his Ape Man mask). They can be worn over large hairdos, large noses, glasses, and hats. This is like the "bigger on the inside" power of Scooby-Doo's doghouse.
- Costumes can hide the form of a large person and make them appear smaller. Examples include the skeletal arms of the Ghost of Buster McMuttMauler and the spindly arms and legs of Stinkweed. If the contrast would too extreme, the villain may be captured in a way that leaves only their head showing at the time of the unmasking.
- A more extreme example is the costume that gave J.C. Chasez the form and four-legged running skills of Scooby-Doo, while his extras impersonating the gang gained super-strength.
- They can also make a smaller person larger, often on stilts inside the costume and/or with huge bodies surrounding the real person, with no difficulties in running or moving their hands and arms.
- A mask of a real person allows near-perfect impersonation, fooling even people who know them well, in broad daylight.
- No matter how it appeared when worn or what properties it had, the mask become soft and rubbery on removal, and the eye and mouth holes usually appear as empty holes.