Roy Koopa is one of the Koopalings appearing in Mario and Luigi: Superstar Saga; during Bowletta's invasion of the Beanbean Kingdom, Roy acted as a guard in Bowser's Castle, which Bowletta had hijacked.
After making their way through Roy's puzzle filled room, Mario and Luigi approached the Koopaling, who fled at the sight of them. Leaving Roy's room, thinking the Koopaling had turned coward, Mario and Luigi were sneak attacked by the oversized Koopaling.
In this battle, Roy would attack by spitting fireballs, spinning in his shell, and stomping the ground, sending shockwaves at Mario and Luigi. Despite having the aid of a Time Bob-Omb in battle, Roy was still defeated by the combined might of the Mario Bros.