The title refers to the Pied Piper of Hamelin, a legend about the abduction of many children from the town of Hamelin, Germany and used in stories written by the Brothers Grimm and Robert Browning.
The Pied Piper in this episode is similar in abilities to a villain from The Flash's "Rogue's Gallery" in the comics. They even share the same initials (H.R.). The similarity ends there.
Bob Hastings was familiar to the DC Universe, as he had previously provided the voice of Superboy in "The Adventures of Superboy" and other series in the late '60s. He would later lend his voice to several Batman animated series and movies in the '90s, keeping him in the DC Universe as Commissioner Jim Gordon.
Eve Plumb (Elena) co-starred as Jan Brady in "The Brady Bunch" (1969 - 1974). Denny Miller (Carl Schwartz) appeared in "The Brady Bunch" episode, "Quarterback Sneak" (s5e9, 1973) as Tank Gates, Carol Brady's (Florence Henderson) former high school boyfriend, but shared no scenes with Plumb.
"The Brady Bunch's" Eve Plumb (aka Jan Brady) makes an appearance in "Wonder Woman", in "The Pied Piper" episode (1977). This is ironic because this was not the only time Eve Plumb interacted with Wonder Woman. Wonder Woman had also appeared in "The Brady Kids" (1972) animated series, in which Plumb gave her voice. That was the first appearance of Wonder Woman in any television program, although Wonder Girl had appeared in the animated "Teen Titans" (1967) show.