Fillerbunny, as suggested by his name, was originally created to fill up space. He has a very rushed appearance and appears poorly drawn. Eventually, Fillerbunny received its own comic, which Jhonen Vasquez claimed he only drew up hours before the deadline.
This was also the case in the second Fillerbunny comic released. However, in his third Fillerbunny comic, which was released in 2005, he changed this method and spent months working on it, which was a hit with some fans, but a sort of disappointment to others, who believed this ruined the theme of Fillerbunny being rushed and perhaps poorly drawn.
Fillerbunny made a cameo appearance in Invader Zim as a dashboard accessory on the bus in Walk of Doom, and another one at the beginning of Dark Harvest, in a jar filled with liquid: Carol Millican set his jar down on a counter near an open window. A dodgeball came through the window and smashed his jar, decapitating Fillerbunny; he appeared again in Issue 15 of the Invader Zim comic series.
- GIR and Fillerbunny were both seen riding pigs at least once.
- Fillerbunny's appearance in Dark Harvest is reminiscent of his native comics, as an ambiguous "lab rat" tormented by his captors for little to no reason.