Charging Dragon (3.5e Equipment)
From D&D Wiki
Charging Dragon: This trap activates when it detects a person nearby (Symbol of Warding, Arcane Eye, ect.). A huge dragon appears and swats at the people. If someone gets hit, they fly to the wall and take 3d6 points of damage. In reality, the dragon is an illusion, and it's claws are actually boulders controlled by a crystal on the wall with Telekinesis.