Monsters vs. Aliens: Mutant Pumpkins from Outer Space is a Halloween special that premiered on RTÉ One on October 26, 2009. It is premiered on NBC in the USA on October 28, 2009.
Susan and the fellow monsters go back to Susan's home just in time for Halloween celebrations. Susan spends time with her parents, while the other monsters join in trick-or-treating and collect a large amount of candies. Later, it is revealed that the monsters came to destroy mutant pumpkins hidden in the halloween decorations. When the pumpkins begin to eat children's candies to grow larger (this Dr. Cockroach had revealed, "It's not the children they're after, it's the candy!"), the monsters and children defeat them by throwing excessive candies to bloat them up and explode them.
However, in a twist ending, some of the pumpkin "blood" (a green goo) falls into a planting of carrots, making a mutant carrot be formed.