What Could Have Been: Various concept art on the website shows different elements that were discarded from the game. Some of these include:
The game itself was pitched in concept as "The World of Bugs" for its name.
Kwincy's baby form always had a single eye, but concept designs made it almost as big as his face, rather than the small size it is now. He also had only a single antenna at this point, swirled to look like a baby hair curl. This design was later reused as his "Kwincy Jr." costume.
Lapoleon was originally designed to have his head and body parallel to each other, without his large chin and defined head that he has now. Other concepts had further evolutions as an upper-crust gentleman over a king, with a top hat, bow tie, and cigar.
Some slug variants were suggested, but never came to the game. These include a knight slug, a fire slug, and a speedy slug.
The Other Darrin: Starting with "Temper's Adventure", Phil La Marr replaces Mark Hamill as Temper. The episode lampshades this change, as Gordon points out that Temper's just cranky "since [his] voice changed".