Ecco, who's based on Harley Quinn, uses that character's catchphrase "Puddin'" several times.
The mutant street gang that Bruce and Selina fight in the Dark Zone closely resemble the street gang featured in the comic miniseries 'The Dark Knight Returns', The Mutant leader utters the phrase: "Slice and dice" which is a known phrase used by the Mutants in that miniseries.
This is the first time Selina has added claws to her outfit.
Francesca has stated that she watched some clips of Suicide Squad and Batman: The Animated Series to have an idea of what Ecco's voice was supposed to sound like, she eventually chose to go for her own way about the character's voice pitch, and then the physical and facial movements.
Francesca was called back to read the script of this episode to make sure she was a good fit for playing Ecco after she shot herself, since the character in Season 4 was the opposite of what she's been in Season 5.