Originally, The Human Torch was going to be in the series with Spiderman and Iceman. Licensing issues at the time prevented the use of the Human Torch and so Firestar was created to fill the open spot.
In the first season episode "Videoman", the ending was vague as to whether or not the villain of the episode (Electro) died at the end. Being a Saturday morning cartoon, they made up for it by having Electro make a cameo appearance in the third season episode "Attack of the Arachnoid" (in a super-powered jail cell, no less!). Only three villains made return appearances after their first appearance on "Spider-Man and his Amazing Friends": Magneto (In a brief flashback in the episode "A Firestar is Born"), Electro (As mentioned above), and Videoman ( Who appeared in "Videoman", "The Origin of Iceman, and "The Education of a Superhero"). Doctor Octopus was the only super-villain to cross over from "The Incredible Hulk" to "Spider-Man and his Amazing Friends" (both cartoons were on NBC on Saturday mornings at the same time). The Human Torch was supposed to be one of the Spider-Friends, but NBC didn't want children to think it was okay to play with fire. That is why Firestar was created, having similar powers, but not having the appearance of being on fire.
The character "Firestar," created for this show, proved so popular that she was inserted into the main-line comic-book continuity as part of the super-villain team "The Hellions" in "The Uncanny X-Men" in 1984. She soon got her own mini-series, and as of 2002, is still a main character in "The Mighty Avengers."
Wolverine's appearance in this show has him speak in an Australian accent, voiced by Neil Ross, despite the character being from Canada in the comics. Wolverine also has an Australian accent and again voiced by Ross in Pryde of the X-Men (1989) which is also in continuity with this series.