This is Milhouse's first appearance in any The Simpsons media. He was created for this short.
There is an alternate version of this commercial. The differences between the two versions can be found in two parts of the commercial:
In the middle of the original commercial, Bart says, "The Butterfinger Group provides the crunchy peanut butter and chocolate-y taste essential for survival." While he says this, a cutaway is shown of a Butterfinger bar slowly breaking in half to show the peanut butter inside. In the revised version, Bart's line has completely redone, now saying "The Butterfinger Group has the chocolate-y, crisp-ity, peanut butter-y taste essential for survival." Meanwhile, the Butterfinger cutaway has changed to new footage of the bar (this time in a wrapper) breaking in half (this time making a sound effect), repeating itself when Bart says the words "crisp-ity" and "peanut".
At the end of the commercial, Bart bites his Butterfinger and swallows it, while an announcer says, "Peanut butter-y Butterfinger." The camera then cuts to a close up a Butterfinger wrapper and zooms out to show it whole. Bart exclaims, "It's neat-o!" The announcer laughs a little before saying, "And it's neat-o." In the alternate version of the commercial, there's no announcer, and Bart bites into his Butterfinger. The commercial then cuts to a Butterfinger wrapper laying on the ground with the words, "Nobody better lay a finger on my Butterfinger!" appear overhead, with Bart reading the words. The commercial cuts back to Bart swallowing the Butterfinger.