Once Goku evolved, the demon smiled and thought that he could use that energy to turn goku on everyone else. Goku lunged, only to vanish behind the demon and land a punch so powerful that the center of the earth became unstable, this energy fired back on goku with a fire filled blaze which sent Goku to the ground gasping for air. The demon filled goku with a dark energy and they both disappeared. Vegeta saw everything and muttered "god dammit."
2 days later
A mist followed by a storm flew through the air as a red eyed Goku flew down and began destroying everything without even thinking twice about mercilessly slaughtering people. Vegeta and Gohan got word of this and headed out to stop the slaughter.