Roar is a monster and the major antagonist of the episode "Frankengloom". The Glooms created him from a kit in order to scare away Queen Delightful from her castle, but that soon backfired as the Queen became his friend and steered him towards a music career.
In a way, Roar looks reptilian, with a ribbed belly and webbed hands. He has red eyes.
According to the Make Your Own Monster Kit, Roar can be full of rage and causes destruction whenever he hears a whistle, whereas he can also be calm when he hears the sound of a bell. His body turns red when he turns enraged, and blue/purple when he's docile. He eventually realizes he has a bright future ahead in singing and turns on the Glooms.
In the series
Using the Make-You-Own-Monster Kit, the Glooms successfully created the monster, but its appearance is tiny. That is quickly solved when they gave it a lot of food to enlarge him. Hildy gave the monster specific instructions to terrorize Delightful out of her castle and then blows a whistle as a signal to do the deed while in rage. Upon his arrival at the castle, the damage he causes prompted cries of urgency from Lord Starchbottom to the Queen that the monster's on the loose. As the monster enters the music room, however, Delightful is composing a song, and she rings a bell, calming down the monster. She believes the monster (she now calls him Roar) has a great voice for singing, and she wants to showcase him to Pied Piper, a music professor, and to the 7D premiering her new song.
While the 7D is bathing and preparing Roar for that night's performance, the Glooms are on their way to the castle to see his progress. Delightful and Roar are then set to perform with The 7D, Starchy, and Pied in attendance. The song's arrangement calls for a whistle and bell to be used, and during the performance, Roar becomes angry and then calm, making Doc suspicious. The Glooms then enter the room, and while Hildy is angry that Roar didn't do the deed of sending Delightful away, she uses the whistle. In return, the 7D use bells of their own and Doc encourages Roar to fight it as this goes back and forth. Finally, Roar has enough and now that singing is his true ambition, he threw the Glooms to the castle moat. In the end, Roar is now a pupil at Pied's school and has a girlfriend named Aah.