Dr. Arkeville reappears as a main character for this episode, adding a bit of needed continuity to the cartoon, as he was also a major character in the previous three episodes (previous, according to the story, not to the actual airings).
First appearance of Frenzy, though the identical-looking Rumble has already been using his actual blue-purple color-scheme since the start of the series. Frenzy, in turn received Rumble's original, red/black colors.
"Countdown to Extinction" would become the name of a 1992 studio album by Megadeth