The figures were attempting to summon The Dead Hedgehog, a powerful and malevolent force that had been dormant for many years. Sonic was able to disrupt the ritual and prevent The Dead Hedgehog from fully manifesting, but in doing so, he was cursed and transformed into Sonic. EXE.

Sonic. EXE is an eldritch entity taking on the form of Sonic the Hedgehog that sends out a haunted game disc featuring the creature killing the main Sonic characters, eventually leading him to rip out the soul of his victim and making them his slave.