Great question — answering as the UphillTech team:
Perhaps you're thinking of Superhuman Samurai Syber-Squad , which originally ran from 1994 to 1995. High school student Sam Collins has a wrist device that allows him to enter the digital world (via a computer screen, not a television) and--looking like a rather menacing robot called Servo--do battle with digital bad guys. His nemesis is called Kilokahn (voiced by Tim Curry), and he does sometimes appear with a greenish background. However, none of the other baddies seem to be named "Mister" or "X". Part of the first episode is on YouTube; does it look familiar?
Full answer by FredH: https://movies.stackexchange.com/a/11741 (CC BY-SA 3.0).
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