Mr. Bun Bun is the main antagonist in Underfist: Halloween Bash.
Much of his background is unknown but he did mention that the other marshmallow bunnies called him soft. He seems to be an crazed egomaniac. He is also highly immature, making fun of Irwin for correcting his grammar in a very childish manner.
Bun-Bun is a marshmallow bunny that tried to rule the world but failed because of Underfist. He did several things that really hurt some of the characters. These are:
- Haunting Hoss when he was young and made him hate all monsters.
- Putting a witch worm in Mindy's hair turning her into a witch.
- Making Billy afraid of spiders so he would not love Jeff.
- Sawing off Fred's tusks (he didn't seem to care)
It's unknown why he scared Hoss, made Billy afraid of spiders and sawed Fred's tusks off, as none of those deeds served any main purpose for him. Though, given how cruel and villainous he is, it's likely that he did this as sadistic pleasure.
He later recruited Skarr to help him rule the world, but Skarr betrayed him and kicked him in pot of hot cocoa and he melted to his death. Before disappearing, he took the form of a vapor and angrily yells out "What did I ever do to you guys?" and vanishes.
- Irwin points out the strangeness of a marshmallow bunny being in a Halloween special, since marshmallow bunnies are considered Easter treats.
- During the end credits, there is a scene entitled “Underfist: Easter Beatdown” where a similar rabbit appears. The most notable difference is that the rabbit appears to be real instead of marshmallow.
- It is unknown whether this is a completely different character or a Bun-Bun reincarnated character to reappear after his destruction in the canceled series.