The original series of Yu-Gi-Oh produced some interesting rivals, while you can argue that Haga and Ryuzaki (Weevil and Rex) are fairly credible threats while Kajiki and Kotsuzuka (Mako and Bonz) were at least interesting, then there's Esper Roba.

Roba was introduced in Battle City as one of many duelists Jounouchi had to defeat to progress to the last eight, he gave the impression that he had clairvoyance and was able to see everything in Jounouchi's hand, unfortunately for the green haired duelist, Roba was exposed as a fake, his younger brothers spying for him and reporting through radio.
A generic design that would barely pass for a background character by Yu-Gi-Oh standards, probably the most annoying dub voice I've ever heard as he has no indoor voice and his motives were basically to stop bullying by making Roba seem invincible, while admirable it does require Roba to actually get away with it, being exposed won't make the bullying stop.
His only redeeming feature is that he has Jinzo which was portrayed better by one of the big 5 and the fact that Roba had to give up Jinzo to Jounouchi.
You could replace him with an actual psychic and they would've been far more tolerable, for a series that prides itself on having the most wild anime designs, this is a big miss for them.