It was a tall, green and scaly humaniod beast resembling Shaggy with claws and a tail.
It constantly destroyed things, as if they were insignificant items.
Powers and abilities
It was extremely strong.
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Shaggy was supposedly cursed after eating a pizza with a transformation spell cast on it by the Ancient One. Shaggy chained himself up that night to ensure that he stays in bed.
The gang had to run from the Tokyo police because of this, as they wanted to get to the bottom of the 30 Foot Shaggy mystery.
The next night, the gang stayed at a hotel with Shaggy sleeping in the vault for safety. Suddenly, they heard a loud crash from the lobby, and discovered the monster outside as it tried to crush them. Fortunately, they were saved by Velma's invention Dogbot just in time, and the monster continued it's rampage until the sun came up.
When they went back to Akira's Robotic Factory, they found the monster inside and proceeded after Shaggy and Scooby. Scooby used Dogbot to change into rickshaw mode, which the monster stepped onto and rolled around until it slipped and crashed. It was revealed to be a giant robot operated by Professor Pomfrit.