The Gangs

The Mudlarks:
A zealous, holy order that exists to protect the purity of the Flow from the corruption of the Donlon underworld.
They wear tattered robes as a badge of honour , it means they have taken on the murk of the city and kept it from the river.
Their devotion is expressed through prayer in ancient Ratin, over vials of Flowater worn around the neck.
They consider the tea trade a cardinal sin, tea impurifies the Flow.
They also hold that throwing bodies into the Flow is a cardinal sin 
They are 'hard to get a read on,' according to Rover, but they have eyes and ears across the city.
The High Purifier leads the church.
Silt Saint Vulpin is a senior operative, he was a Tide Priest in the past.
Carlos is a Tide Priest.  
There are also Flowcombers, probably a very low class among the Mudlarks.

The Bigwhigs: 
The ruling political class of Donlon.
Ballooning caricature-like figures with long powdered wigs and heads stuffed with immense magical power.
They sit in Whitehall and control the city's official power structures.
The most powerful Bigwhig is Arch Minister Reginald Toby Punch, who has access to magic so powerful he could curse Danny, changing him into a bulldog.
The Porcelain Police operate under the Bigwhig authority structure. 

The Carnabal: 
Fae tricksters and schemers dancing between royal intrigue and show-stopping circus flair.  The Carnabal are circus-like performers.
The Carnabal's centaur bodyguards carry tattoos that shift and dance on their skin, powered by enchanting magic that is nearly entrancing to watch.
When you are a big act in the Queenly Court, you are so much more. 
The Mercury is their leader
The Queenly Court has a strong interest in the Black Tea.
In episode 2 they sent Bronwyn and Caerdwen to intercept the party and seize the package for the Mercury.
Maureen has history with the Queenly Court as a performer and knows Bronwyn and Caerdwen personally. 

The Twilight Twins:
The most dangerous act in the Carnabal. Bodyguarded by Bronwyn and Caerdwen.
Arrived at the episode 2 cliffhanger announced by a hunting horn, landing in a perfect gymnast's poise.
In episode 3 they are called assassins. 

The Street Genies: 
A gang of rebels and firebrands.
They capture djinn (genies) and pressurise them into canisters worn on their backs, syphoning the magic into their velocipedes (penny-farthings).
The bikes leave Tron-like coloured streaks as they move at extraordinary speed.
Elemental attacks: icy blue (cold), flame, acid, and wind.
Tag Magic: When defeated in combat, Street Genies dissolve into 2D street art, graffiti versions of themselves that can still move along surfaces.

The Mobgoblins
The most powerful gang in the East End.
All crooked-toothed, ham-fisted goblins, giants, goliaths, and orcs.
Their foot soldiers are put through the brutal baptism of the fighting pits to make the Mob one of the fiercest forces in Donlon.
In the old days, under Albert Krag, the Mob had a code, honour among thieves, genuine community in the East End.
The twins destroyed that code when they devoured Albert and took over.
Under Phil and Grant, the Mob became wantonly violent.  The Mob now runs the tea trade across much of the city.