To call Red X a supervillain is somewhat of a misnomer, but that's only because the character's role in the original Teen ...

While Cartoon Network's 2003 Teen Titans ... priority of the episode quickly becomes about Raven regaining her senses so as not to seriously endanger anyone else. When the Titans battle allies ...

Red X first appeared in the 2003 Teen Titans episode “Masks,” where Robin created the identity to infiltrate Slade’s criminal organization. Wearing a black suit powered by unstable xenothium ...

which has run for eight seasons and over 400 episodes. That show, and its early '00s predecessor Teen Titans animated series center on a core cast of Robin (Tim Drake), Cyborg, Raven, Beast Boy ...