Compared to other toy-based cartoons, Challenge of the Gobots took an unusual approach. Rather than spreading screen time among the toys, it picked six and largely stuck to them. Three full regulars were chosen from each side - Leader-1, Turbo and Scooter for the Guardians; Cy-Kill, Crasher and Cop-Tur from the Renegades. The three Guardians were ever-present, while the Renegade regulars only missed one or two episodes each.
After the 'big six', very few Gobots appeared in more than a dozen episodes. Some were more frequently seen than others, with the likes of Fitor, Zeemon, Small Foot and Blaster managing to appear in 20-25 episodes (which is still only around a third). The format was generally that the regulars would be joined by 'guest' Gobots - usually an additional Guardian joining the usual trio on Earth, and two or three henchmen for Cy-Kill. An exception was episodes largely set on Gobotron, which would often feature bumper casts (though most of them wouldn't do much).
At the other end of the scale were some characters who featured in only a mere handful of episodes - these varied from the likes of Dive-Dive and Zero, who would effectively get 'spotlight' appearances, to Spoons, Crain Brain, Dumper or Defendor, who would appear in minor background roles a couple of times and then disappear, never to be seen again. There were varying reasons for this - by the time the TV series was being created, Tonka were already discontinuing some of the poorer sellers from the first year of the toyline. Similarly, the toys continued to be made after the cartoon would end, and many new characters only arrived in time for the last few episodes. Some just weren't used that much for no readily apparent reason.
Hanna-Barbera would also devise two fully-fledged Gobots - Steamer, a Renegade who defected to the Guardians, and Wrecks, an old Gobot who looked after the dropouts in Old Gobotron. They also designed numerous generic civilian Gobots to pad out scenes on Gobotron. Another slight oddity was Snoop - the toy she was based on failed to come out in America for unknown reasons (it was released in Japan and Europe), yet she turned up in several episodes, with a key role in one.
Several toy characters never appeared in the cartoon: