In the Animation, when the events of the M’arrillian Invasion effectively began, Phelphor mind-controls the Guardians of the Deepmines, Vinta, Junda, Nauthilax and Tartarek, so they could open the Doors of the Deepmines. Brainwashed, comes into play the Psi-Overloader.
As a M’arrillian Minion, not only Tartarek became faster and more resilient, but he now masters both Fire and Earth Elements too, maximizing the damage caused by Attacks like Lavalanche. But the most impressive — and sometimes considered overpowered — of the Psi-Overloader’s traits is that one of his new abilities allows him to defeat a M’arrillian Chieftain as smart as him with a single move, at any time. This means that Creatures like Rath’tab or even the mightiest version of Aa’une, the Avatar seen in the final battle during the events of Legions of Aa’une, aren’t a match for him. An ability inversely proportional to Fal’makin’s, another of the M’arrillians Chieftains, so dangerous to the M’arrillians that was likely the reason Tartarek was brainwashed to start with.
In the Animation, nobody suspected that Tartarek had been brainwashed until it was too late, a perfect disguise that allowed him to fool everyone with an apparently perfect master-plan to defeat the M’arrillians. That only happened because, differently from other Minions, the Psi-Overloader remains in the character, undercover, by using his new abilities as he sees fit, regardless of a Chieftain command.
And on top of all that, at expense of a Mugician, he’s also capable of boosting Creatures’ Wisdom, be it to help a squadmate or to stealthily make an opponent meet the requirement needed to be dealt with single-handedly.
Tartarek, Psi-Overloader is almost considered a compact War Beast, only with no Recklessness.