After Jim Gordon arrests a criminal carrying one of Penguin's licenses, Arthur Penn visits Bullock at his office. Penn tells Bullock that Penguin worries about Jim being compliant, but Bullock assures him that the GCPD will honor the licenses.
Arthur Penn informs Penguin that 14 percent of crimes are happening outside of his Pax Penguina. Sofia Falcone comes in and asks Penguin to come with her to lunch. Sofia tells him that it would show everyone that he has the support of the Falcone family, which could help to get him 100 percent compliance.
Jim comes into The Iceberg Lounge, to see if Penguin has any leads on Officer Dave Metzger's murder. Arthur Penn informs Jim that a man named Wally Clarke recently applied for a burglary permit for a butcher shop called The Pork Barrel. Later, Zsasz and Penn present Penguin with evidence that Sofia seems to be up to something behind his back. Penguin tells Zsasz they will "visit" Sofia immediately and find out what she's doing.
The Sirens raid the Iceberg Lounge at the time when Arthur Penn was waiting for Cobblepot to send further instructions. Tabitha Galavan tortures Penn on where Cobblepot is. She is unable to get any information out of him.
While looking for something they can use on Sofia Falcone, Harvey Bullock meets with Carmine Falcone's former Scandinavian hitperson Agnes who directs them to Arthur Penn. When encountering Oswald Cobblepot on the streets after Edward Nygma helped him escape from Arkham Asylum, he informs them that Arthur Penn tends to frequent a resort called the Spa Bo'sh Sumka outside of Gotham City near the Tricorner island. As Gordon and Bullock head there, Sofia gets word from Victor Zsasz and Headhunter that Arthur Penn is at Spa Bo'sh Sumka causing Sofia to lead them and some Falcone crime family members there. Gordon and Bullock find Arthur Penn there amongst the baby-dressed patrons. Penn states that he used to work for Carmine Falcone before his retirement. When he worked for Cobblepot, he had to also work for Sofia Falcone when he was threatened by her. In addition, Penn mentioned that he was the one who told Carmine what his daughter was doing. Just then, Sofia shows up with Zsasz, Headhunter, and some unnamed Falcone crime family members. Headhunter, Zsasz, and Sofia end up in a gunfight with Gordon and Bullock. While Sofia fought Gordon, Headhunter and Zsasz chased after Bullock and Penn. After the two of them escaped in Lee Thompkins's car, the Zsasz and Headhunter gave up pursuit and went to get smoothies when they saw the police cars come into view.
- Accountancy: Penn is an incredibly skilled accountant, able to keep track of the finances and transactions of whole criminal empires. He was also given the task of assembling the crime licenses during the Pax Penguina.
- Triple agency: Arthur managed to secretly work for three powerful crime lords at the same time, namely Oswald Cobblepot, Carmine Falcone and Sofia Falcone. He was mainly Penguin's accountant, but also informed Don Falcone about Sofia's actions when she came to Gotham. However, Sofia found out and only let Arthur live when he offered her to be her informant in Cobblepot's crime family. However, Penn was still loyal to Carmine and Penguin, since he informed Don Falcone about Sofia's connection with Professor Pyg and advised Oswald to order a hit on Sofia.
- Network: Due to his history as the accountant of several mob bosses over the course of many years, Arthur has access and connections to various crime families and gangsters. He was the one who put Sofia Falcone in contact with professional contract hitman Lazlo Valentin.
- Survival expert: Penn has wide knowledge of how to stay alive in the mob business, as shown when he offered Sofia to be her informant in the Cobblepot crime family, knowing that she would accept this offer and keep him alive for that task. He is also aware of the fact that a bearer of bad news often gets blamed by crime lords and becomes a victim of 'shooting the messenger', therefore he quickly leaves as soon as he delivers unpleasant information.
- Master tactician: He was capable of hiding his affiliation with Sofia Falcone from experienced crime bosses Carmine Falcone and Penguin. Penn also cleverly tried to eliminate Sofia by proxy by advising Cobblepot to have her killed by Victor Zsasz.
- Leadership: Arthur has at least some rudimentary leader skills, as shown when he managed to organize the remaining henchmen at the Iceberg Lounge during Penguin's absence and ordered them to wait for Cobblepot to send further instructions.
- "A Dark Knight: Pax Penguina"
- "A Dark Knight: The Blade's Path"
- "A Dark Knight: Hog Day Afternoon"
- "A Dark Knight: Stop Hitting Yourself"
- "A Dark Knight: Let Them Eat Pie"
- "A Dark Knight: Queen Takes Knight"
- "A Dark Knight: The Sinking Ship, The Grand Applause"
- The character was intended to become the show's version of the Ventriloquist in Season 5, with the actor even hinting at the role. However Ventriloquist and Scarface were later omitted out of the season, but Easter Eggs relating to the character will be shown instead.
- ↑ Stephens, John (writer) & Cannon, Danny (director) (September 21, 2017). "A Dark Knight: Pax Penguina". Gotham. Season 4. Episode 1. FOX.
- ↑ Chun, Tze (writer) & White, Scott (director) (October 19, 2017) "A Dark Knight: The Blade's Path". Gotham. Season 4. Episode 5. FOX.
- ↑ Newton, Kim (writer) & Tonderai, Mark (director) (October 26, 2017) "A Dark Knight: Hog Day Afternoon". Gotham. Season 4. Episode 6. FOX.
- ↑ Cannon, Danny (writer) & Stephens, John (director) (December 7, 2017) "A Dark Knight: Queen Takes Knight". Gotham. Season 4. Episode 11. FOX.
- ↑ Boston, Seth (writer) & Copus, Nick (director) (March 22, 2018) "A Dark Knight: The Sinking Ship, The Grand Applause". Gotham. Season 4. Episode 15.