Rrarrg is a light blue, toxic waste monster with a light purple backside, lavender arms, and legs, along with a tan belly. Rrarrg also has barnacles growing on his back, chap dark purple lips, and chipped teeth.
Despite his intimidating appearance, Rrarrg is actually quite friendly. He shares many interests and hobbies with Patrick, such as sniffing his own armpits and playing catch and hide-and-seek.
He seems to have a sensitivity to raised sensory, as exemplified when he loses his mentality over hearing a police officer sneeze into a megaphone.
"The Monster Who Came to Bikini Bottom"
Rrarrg appears as the main antagonist of the episode. Patrick accidentally opens a toxic waste can which pours radioactive waste on a group of purple barnacles, which causes them to fuse together to become a giant monster.
Patrick and Rrarrg then become friends and start engaging in many childish activities to pass the time. Patrick is eager for SpongeBob to meet his new friend, so he jumps into the monster's mouth and rides over to SpongeBob's house. Patrick then introduces the monster to SpongeBob, who finds out that the monster's name is Rrarrg. Patrick allows Rrarrg to live under his rock, but the monster - being too big to be accommodated - ends up breaking it instead.
Rrarrg then destroys the other two houses on Conch Street and is subsequently put under captivity by the police. When a cop sneezes in the megaphone, Rrarrg goes berserk. He then runs through Bikini Bottom and the police finally catch him and drive him out of town. However, SpongeBob has an idea: They transport Rrarrg and Patrick to a snowy mountain to get ice for the customers at the Krusty Krab. Whenever a customer needs ice, SpongeBob just calls Patrick for Rrarrg to smash a big block of it and to throw the cubes to the Krusty Krab when the ice machine is broken.
"Things to Do When Encountering Legendary Creatures"
He appears at the end of the short. He appears as the monster at the end. SpongeBob and Patrick run away from him, thinking he is mean. He then sheds a tear because he is lonely.