|01 "Year Zero"||07 "Ace Chemicals"|
|02 "Trespassers"||08 "Nothing's Shocking"|
|03 "Penguin, Our Hero"||09 "The Trial of Jim Gordon"|
|04 "Ruin"||10 "I Am Bane"|
|05 "Pena Dura"||11 "They Did What?"|
|06 "13 Stitches"||12 "The Beginning..."|
- For the chemical plant the episode is named after, see Ace Chemicals.
- "Why don't you understand? You need me. I'm the answer to your life's question! Without me, you're just a joke... without a punchline."
- —Jeremiah Valeska to Bruce Wayne
Gordon races to uncover the criminal element threatening to end talks of Gotham's reunification with the mainland. A very much alive Jeremiah returns and organizes a twisted recreation of the murder of Bruce's parents with the help of Jervis Tetch.
- Prior to the episode's airing, the tie-in novel Gotham: Dawn of Darkness depicted Bruce and his parents finishing a film before leaving the theater and subsequently encountering Matches Malone. The events of the episode contradicts this somewhat, as Bruce is revealed to have been too scared to even finish the film, thus leaving the theater early, a detail seemingly made to homage depictions such as the film Batman Begins, where Bruce's fears play a role on the fateful night.
- The Mad Hatter last appeared in "A Dark Knight: That's Entertainment".
- This episode marks Benedict Samuel's final appearance as Mad Hatter on the show.
- This marks the first appearance of the Ace Chemicals plant since the season 2 episode "Wrath of the Villains: A Dead Man Feels No Cold".
- Although Martha and Thomas Wayne do not reappear in the flesh, they are impersonated by lookalikes played by the same respective actors from the pilot. This episode marks the first time that actors Grayson McCouch and Brette Taylor have filmed any new scenes since the first episode.
- This episode was promoted with a special Happy Valentine's Day From Mr. J & Ecco trailer, which was released on Valentine's Day 2019. The trailer highlighted the mad love between Jeremiah and Ecco. It was also the first trailer to reveal Mr. J's voice from the series finale, as he is heard saying the line "Dear me, my sweet Ecco". The song played during the trailer is called "Honey Bunny" by Orchestra Charlie Steinmann.
- The Wayne Manor study set has its final appearance on the show. After filming for "Ace Chemicals" had wrapped, the Wayne Manor set was partially demolished and redressed to depict an abandoned mansion in North Side Park where Bruce and Jim are interrogated by Nyssa and Bane in the episode "Legend of the Dark Knight: I Am Bane".
- The Destruction of the Wayne Manor is an allusion to various comics and adaptions of the Batman mythos: It had been destroyed in the 1986 Frank Miller comic The Dark Knight Returns (as well as in the 2013 animated adaption), the 1991 Elseworlds story Batman & Dracula: Red Rain, and the 1996 Kingdom Come future. Like in Gotham, the Wayne Manor was also destroyed during No Man's Land in the original comics: In the 1998 storyline Batman: Cataclym that set up No Man's Land, Wayne Manor was completely destroyed when an earthquake hit Gotham City. Similar to Gotham, the Batcave was also heavily damaged and buried under the ruins.
- This marked the third time that the Destruction of Wayne Manor had been portrayed in a live-action adaption, following the 2005 movie Batman Begins and the 2016 DCEU movie Batman V. Superman: Dawn of Justice, in which it is shown that the Wayne Manor was abandoned years before the events of the movie following a large fire. Wayne Manor was also destroyed at the end of the 2015 video game Batman: Arkham Knight.
- As confirmed by writer Tze Chun, the coat worn by Bruce Wayne in "Ace Chemicals" and various other Season 5 episodes is a reference to the 1987 comic book story arc Batman: Year One by Frank Miller. In the Year One comic, Bruce Wayne was seen wearing a very similar coat.
- The episode showcases the first onscreen appearance of the Monarch Theatre on the show. Prior to the episode, the theater appeared unnamed in the tie-in novel Gotham: Dawn of Darkness.
- The episode is the first to reveal the 1920 film The Mark of Zorro as the film that Bruce and his parents watched on the night of the murder. Prior to this episode, tie-in materials for the series simply referenced it as a musical.
- It is revealed that Bruce's parents were killed on June 27.
- When Jeremiah's reenactment of The Mark of Zorro is screened at the Monarch Theatre, it can be seen that Ecco is standing behind him in the black-and-white film. She is seen dancing in a vintage dress in the background while Jeremiah reenacts a fight scene dressed as Zorro. Francesca Root-Dodson has released two color photos of her as Ecco wearing the costume from the scene. This reveals that the costume is based on the outfit Harley Quinn wore in the 2015 video game Batman: Arkham Knight, with Ecco's outfit adopting many elements like the black dress with white ruffle, the black and red leggins, the long evening gloves and the white dress shirt shoulder pieces..
- Jervis Tetch mentions the "tea party" during which Jim Gordon once asked him to kill Lee Thompkins. This is a callback to the events of the episode "Mad City: Follow the White Rabbit", in which Tetch had kidnapped Lee and Valerie Vale and forced Jim to decide which one he loved most so he could kill her in revenge for the death of Alice Tetch.
- Ecco is seen skating on roller skates during the confrontation at Ace Chemicals. This is another direct nod to Harley Quinn. In the comics, roller skates are widely associated with the character and often used by Harley Quinn starting with the New 52 relaunch of the DC Universe.
- The Chessmen originate from the DC Comics and were a street gang that Batman once encountered in Batman: Legends of the Dark Knight #79 (1996). In the comics, the Chessmen stole Bruce Wayne's toy train from Wayne Manor, which was the last christmas present given to him by his parents before their death. Batman later manages to track down the Chessmen and recover the toy train.
- This episode marked the final time Tabitha Galavan was ever mentioned on the show.
- Jeremiah's plan to execute Leslie and Gordon in the alleyway could be a subtle homage to Jack Napier/The Joker being responsible for killing Thomas and Martha in the 1989 Batman movie. In similar fashion, the name of the theater was first established in the same film, later becoming a staple in future Batman media.
- This marked the third time the Joker falling into the chemical vat had been portrayed in a live-action adaption: The first was in the 1989 Tim Burton movie Batman and the second in the 2016 film Suicide Squad. However, Suicide Squad did not potray Joker's origins of him falling into the vat and only showed him jumping into the chemicals to save Harley Quinn. Therefore, Gotham marked the second time the chemical vat origin of the Joker had been portrayed in live-action.
- At Ace Chemicals, a sign on the side of a chemical vat reads "Ace Chemicals 1989". This is an allusion to the 1989 movie Batman, which was the first adaption to feature the chemical bath origin of the Joker. In the 1989 movie, Ace Chemicals was actually renamed Axis Chemicals.
- Valeska's chemicals contaminating the Gotham River is a reference to Detective Comics #475 (February 1978), in which the Joker decides to poison Gotham's water system with his hideous Laughing Toxin, leading to the creation of the infamous Joker Fish.
- At the end of the episode, Penguin and Nygma plan to build a submarine in order to leave Gotham forever. This is a callback to the original Batman movie from 1966, in which Penguin owned a private submarine that was used by him and his allies in that film, Catwoman, Riddler and the Joker. This is further alluded to in later episodes, in which Oswald claims the submarine as his own in subtle ways, to the anger of Nygma: For example, in the episode "Legend of the Dark Knight: Nothing's Shocking", Oswald refers to it as "my" submarine and plans on naming it after his deceased mother. In the episode "Legend of the Dark Knight: I Am Bane", it can be seen that Oswald also added a small portrait painting of himself to the left side of the submarine, alluding to the fact that he considers the submarine his own, just like in the 1966 movie.
- "Ace Chemicals" was the final Gotham episode to be aired in actual production order. When Gotham was cancelled after season 4, Season 5 was originally only going to consist of 10 episodes to wrap things up. "Legend of the Dark Knight: I Am Bane", "Legend of the Dark Knight: They Did What?" and "Legend of the Dark Knight: The Beginning..." were written and produced as the final three episodes of the show. However, during production, Gotham was given two more episodes by the network, bringing the total episode count of the show to 100. These two episodes were produced after filming of the series finale had wrapped and ended up becoming "Legend of the Dark Knight: Nothing's Shocking" and "Legend of the Dark Knight: The Trial of Jim Gordon", two episodes that take place between the events of "Ace Chemicals" and "I Am Bane". Since the final three episodes had already been produced at this point, "Nothing's Shocking" and "The Trial of Jim Gordon" ended up being filler episodes that do not have a greater impact on the overall story.
The original soundtrack for "Ace Chemicals" was composed by David Russo and includes:
- Jeremiah's Grilled Cheese and Branston Pickle Sandwich
- Jeremiah Destroys Wayne Manor
- Jeremiah Almost Kills Gordon and Lee
- Jeremiah into the Vat at Ace Chemicals / Jeremiah Falls Into The Vat