The U78-X/D "Diablon" was a prototype energy-charged weapon built by the Guardian Units of Nations and one of the final bosses in Shadow the Hedgehog. It took the form of a large red mecha that was directly or remotely piloted by the Commander and fought alongside Sonic the Hedgehog against Shadow the Hedgehog after the dark mission was completed in the levels GUN Fortress, Black Comet, and Final Haunt in story mode. Both Sonic the Hedgehog and Diablon were defeated by Shadow the Hedgehog by using the latter's weaknesses against it.