According to the audio commentary for this episode, Joker was going to make an appearance. He was going to be working on a trap for Batman, then Batman would appear holding the pig/Diana, trying to calm it down. The Joker would've seen him talking to the pig, and given up on his plans because he couldn't top that situation. But they decided not to add the scene.
Like in the DC Comics, Zatanna casts spells by speaking backwards: kcab ot lamron (back to normal), lleps eb nekorb (spell be broken), anaiD, emoceb namuh (Diana, become human), esrup raeppa (purse appear), dnufer (refund), stcejbo kcatta ecriC (objects attack Circe), elbat mrof egac (table form cage)
Originally, the plot involved Circe turning the main male Justice League members into animals, with Wonder Woman trying to track them all down while Zatanna pursued after Circe. The idea changed and evolved over time, because it was considered too serious for this type of story.
According to the DVD commentary, Medusa's appearance was based on actress Tallulah Bankhead, and if they hadn't already recorded her dialogue before animating it, the producers would have instructed voice actress Laraine Newman to play the character to match. Ironically, Miss Bankhead's last acting role was on an episode of the Batman (1966) TV series titled, Caught in the Spider's Den (1967).