X-Raycer are Hot Wheels castings that have plastic transparent bodies and a metal base. They are made so that someone could see the details of the engine and interior of the car. However, some cars, such as Vulture, are the reverse of X-raycers, with a plastic, transparent base and windshield while the rest of the car is solid, opaque metal.
Although cars were produced with transparent bodies in the past, the X-Raycers line debuted as a subset of the 2005 First Editions.
It would appear again as a subset in the following years: