The trick-or-treaters were two young boys who appeared in the Halloween episode. One of them wore a Swamp Thing costume and the other one wore a 2007 movie version Optimus Prime costume.
In the Halloween episode, the Angry Video Game Nerd has been asked to babysit a neighbor's young sons during Halloween night. While the Nerd conducts one of his game reviews, two young boys knocks on the door to the Nerd Room. The Nerd opens and finds the two trick-or-treating boys at his door. One of the boys are dressed as Swamp Thing, while the other is Optimus Prime. When they ask for candy, the Nerd pulls up a plastic bag and fills it with his own shit and then tries to pass it off to the kids as chocolate. The trick-or-treaters protests that it's not chocolate, "but poop," to which the Nerd responds with "It's not chocolate, nor is it poop, IT'S SHIT!" The kids are not thrilled and continue to ask for candy, so the Nerd hands his copy of the Halloween video game along with an Atari 2600 console from his shelf.
Later that night, the Nerd goes to the house of the kids that he is supposed to take care of for the night. He discovers that it is the same kids who had come and asked him for candy. The Halloween game happens to be playing on the television screen in the living room as the Nerd enters the house. The Swamp Thing kid calls him "the Poopy Man," to which the Nerd responds "No, no, no! The Poopy Man's more like the Boogeyman and he's going to get you if you don't turn off this game!" The trick-or-treater kids then convinces the Nerd to play the game. While he is playing, they repeatedly hits him with their stuffed animals, saying things like "You suck! You suck! And you smell like poop! You stink!" The Nerd loudly orders them to shut up, but then all the power in the house goes out, frightetning the trick-or-treaters. The Nerd asks the Swamp Thing kid if they have a basement and a circuit breaker. He says yes. While the Nerd walks down a hallway in the kids' basement, he sees the bag of shit he gave to them is lying on the ground. He wrinkles his nose in disgust. The Nerd reaches the circuit breaker and he turns it on, but suddenly Michael Myers steps out of the darkness, jabbing his knife at the Nerd. The Nerd backs away, he reaches down and lifts the bag of shit, swinging it at Michael Myers, splashing his shit onto him. He then runs back to the stairs.
The Swamp Thing kid stands on the stairs with two wireless Atari 2600 controllers in his hands. He throws them to the Nerd, who turns around and jabs their long antennae into the eyes of Michael Myers, who has gained up to them. The Nerd runs up the stairs with the Swamp Thing kid. Michael Myers follows them upstairs.