A mind-controlled Colossus turns the tables on his X-mates when he falls under Arcade’s control in Murderworld!
Reprint of and retroactive backup story to The X-Men #124 - He Only Laughs When I Hurt!(August, 1979).
Backup story summary:
"Play With Me"
Arcade wakes from a nightmare in which he's a child being chased by huge, anthropomorphic toy cars. Realizing it was just a dream, he attempts to regain his wits, but it's a dark and stormy night and he feels like he's hallucinating.
He regains his composure (such as it is), when an alarm alerts him that Murderworld has been activated without his authorization. Investigating from the control room, he finds that his authorization codes no longer work. Infuriated that he's been locked out of his own computer program, he physically enters Murderworld to find out who it's been programmed to kill.
Inside of his creation for the first time, he almost gets eviscerated by a pair of his own robots. Narrowly dodging one, he maneuvers it into decapitating a second before shutting it down with a shotgun. Further in, down an eerily familiar hallway, he's shot at himself by a trio of robots modeled to look like stuffed animals from his childhood, but escapes them by running into a brightly lit room where a young boy is surrounded by a large selection of toys. Realizing that the boy is himself as a child, Arcade attempts to play with him, but the boy breaks the toy that Arcade holds out to play with. Infuriated that the boy is so ungrateful, he raises the toy above his head to hit him with it, but the realizes he'd only be hitting himself and marvels at what an awful brat he was.
Then another robot appears that looks like Arcade's father; the robot doesn't seem to notice him and goes strait for the boy, chastising him for spending all of his time playing and wasting money. As the robot is about to strike the boy with a toy airplane for being so useless, Arcade comes up from behind and smashes it's head in with a toy train.
He then picks the boy up protectively only for it to fall apart in his arms. Now taking the invasion of Murderworld as an obvious attack on him personally, Arcade returns to the control room to hack into his computer and see who had programmed the simulations meant for him. After expressing reactions ranging from enraged, to disgusted, to actually impressed with his foe's sense of humor, he starts breaking the codes that have locked him out. He finds that the new programs were added at 2:am while he slept.
But when he asks the computer who added them, it replies only "USERNAME: ARCADE", leaving Arcade himself completely baffled.