Flash mentions his uncle coming down to spend the Flash Appreciation Day/Flash Museum opening. In the comics, Wally's uncle was Barry Allen, the second Flash and Wally's mentor during his tenure as Kid Flash. The employer in the hospital where he works on investigations - a job Barry Allen actually had in the comics - may have been drawn to reference him.
In some form or another, almost every major villain in the Flash's history appears in this episode, making cameos either at the Rogue's hangout or in depictions at the Flash Museum. The rogues at the bar include Weather Wizard, Turtle-Man, Thinker, Fiddler, Doctor Alchemy, Abra Kadabra, and Pied Piper.