The Dragon was a projection created by thieves.
Physical appearance[]
The dragon had a long neck, dark green spikes on his back, bushy black eyebrows, scales and sharp teeth.
Personality[]
It's apparently easily more terrifying than the previous monster the gang saw, making them focus more on getting away and forgetting to rescue Scooby.
History[]
Scooby Doo... Where Are You! (Charlton Comics)[]
After running out of the Egyptian exhibit from a hairy green creature, the gang searched for Scooby in a room filled with vases and urns, as Scooby was hiding in one of them. But before they could get him out, a large green dragon showed up and spooked the rest of the gang out of the room.
Scooby popped out of the urn expecting to get attacked, but was surprised to find out that the dragon was really a projection created by two random thieves who wanted to rob the museum. And shortly found out they've been using carbon dioxide to project the monsters