He's the fighter from the underworld, back to wreak havoc, make way for RADIATION!
Radiation is one of Mark Hedhon's bots who he won on eBot.
Radiation is powered by radiation itself. It is carefully encased inside Radiation. Radioactive has a powerful move named Radioactive Smash.
One time, When Mark was testing Radiation against Ravagor. Radiation's AI (Artificial Intelligence) created a custom move. It used Radiation's radioaction core to powerfully wreck Ravagor's motherboard. Mark then named this move Radioactive Smash. Mark is still trying to code Radioactive Smash into Ravagor.