The Mutant Toys (sometimes referred to as Sid's Toys) were supporting characters from the first Toy Story movie. They were built by Sid from mixed pieces of several toys that belonged to him and Hannah. They lived in his house, hidden in the dark corners of his room.
When Woody and Buzz Lightyear first encountered them, they thought they were cannibals who were going to eat them, especially when they blocked the escape route for the duo. Holding Buzz as a hostage, Woody pushed the button on his back to make his arm chop to back them away as they tried to escape.
However, when the mutant toys later placed Buzz's severed arm back in place, as well as taping the heads of Hannah's Jane doll and Sid's toy Pteranodon back to their correct bodies, Woody was stunned to see that they were not cannibals as he had initially thought them to be. After Sid took Buzz (whom he had strapped his new rocket to) outside to be blown up, the mutant toys agreed to cooperate with Woody in his plan rescue Buzz from Sid's clutches while also seeing this as their own chance to get revenge on him. Working together, they first drove Sid's dog, Scud, who had stationed himself outside Sid's room, away and out onto the front porch so they could safely escape into the backyard. Once outside, they moved into their final positions, from where they emerged out, surrounding Sid, as Woody told him how much they don't like being mutilated and that they'll find out if he didn't take good care of his toys because "we toys can see everything." After Woody scared Sid away with his own voice, "So play nice," and caused him to retreat in fear of his own toys (considering everything he had done to all of them), they all rejoiced victoriously.