The following is a list of characters who have only been mentioned on Rock, Paper, Scissors.
Dirtbag Joel[]
Dirtbag Joel is mentioned by Scissors as a friend of his who lives in Canada. He is first mentioned in "Birthday Police", when Scissors suggests that the trio hide out in Canada with him, and stating that, despite his nickname, Joel is a terrible person. Later in the same episode, Rock mentions that he doesn't have a good Birthday Lawyer, and Scissors recommends Dirtbag Joel.
Shrodder[]
Shrodder is mentioned in "Weekend Story" as a villain that Paper and the Pre-Teen Modified Martial Arts Tortoises had to defeat to save the city from an unspecified peril Shrodder caused it. He is a parody of Shredder from the Teenage Mutant Ninja Turtles franchise.
Grandma Rock[]
Just before Rock finishes his weekend story to Pencil in "Weekend Story", Rock remembers the last thing that Grandma Rock ever said to him: "Never buy red."
Paper's mom[]
In "The Arctic", Paper mentions his mom, and suggests that he, Rock, and Scissors stay at her place instead of staying in their freezing apartment. However, this plan was quickly abandoned when he couldn't open the door, which had been frozen shut.
Officer Wishkowski's mom[]
In "Birthday Police", Officer Wishkowski mentions her mom. She also mentions that her mom owned a bakery that gave out free cake on people's birthdays. This however, proved not to be a wise decision, as people started taking advantage of it, causing Wishowski's mom to lose 6 or 7 dollars a month (which added up, as Wishowski describes).