Jonathan Sims - Absolutely paranoid after the worms, stalking his coworkers, breaking and entering, et cetera. He is not making friends this way. The police are investigating him for Gertrude's murder.
Martin Blackwood - The guy who lived in de archives for a while last season. He can best be described as a kind, caring, tea drinking person. Both Jon an Tim are kinda mean to him for seemingly no reason.
Tim Stoker - Very fun and outgoing guy in season 1, but has been getting more and more depressed. He wants to quit his job at the Magnus Institute, but something supernatural is making this physically impossible.
Sasha James - Also a very fun and outgoing person in season 1, but is a lot more calm and private now. She spends a lot of time at Madame Tussauds with her new boyfriend Tom (who looks like a stock photo lol), who works there. She has some authentication problems with her computer.
Elias Bouchard - Head of the institute. Like the others, he tries to help Jon with his paranoia and intervenes when he goes to far. Jon does not like that.
Basira Hussain - The police officer who provides Jon with some of the tapes that were found near Gertrude's body in the tunnels. She is sectioned (Section 31 - a form you have to sign when you were involved in supernatural police cases).
Alice 'Daisy' Tonner - The detective who works together with Basira, because she is also sectioned. She deals with vampires (the ones described by vampire hunter Trevor Herbert in his statement). She's very strong and kinda scary.
Melanie King - Paranormal investigator from youtube channel Ghost Hunt UK. She and Jon do not get along.
'Michael' - First introduced helping Sasha and the others with the worms. He looks kind of human but slightly off, and staring at it or hearing its laugh makes your head hurt. His hands are too long. Sometimes, he manifests in the form of a yellow door that leads to endless corridors. From the wiki: 'Michael alludes to a war that was being fought and claims the destruction of The Magnus Institute would sway the war too much in one way. It asserts itself to be a primarily neutral party in the conflict but says he helped The Magnus Institute defeat Jane Prentiss to indulge his own curiosity.'
Gertrude Robinson - Head Archivist of the Magnus Institute before Jon. Her body is discovered together with a box of tapes in the tunnels, by Martin during the Prentiss attack.
Gerard Keay - Son of Mary Keay and Eric Delano (former assistant of Gertrude). Described as having long, badly dyed black hair, eye tattoos on every joint (that don't get burned like the rest of his body in MAG12). He often appears in statements related to Leitners but is rarely mentioned by name. Trust him, he's cool.
Mary Keay - Gerard's mother. She is an older woman with writing all over her body. She owns a lot of Leitners. Don't trust her, she's scary.
Simon Fairchild - Really old man with a lot of money who likes (sky)diving.
Michael 'Mike' Crew - Has a lichtenberg figure (lightning) scar running across his neck and back and smells like ozone. He likes falling and throwing people off buildings. When someone says 'Mike', this is the one they're talking about, 'Michael' is the one with the doors.
Adelard Dekker - He occasionally assisted Gertrude.
Sir Robert Smirke - an architect in the 1800's. Buildings of his design show up more than others in statements.
Breekon & Hope - Two very tall and imposing looking delivery men with an exaggerated cockney accent and a white van. They often feature in statements transporting weird/cursed items, like the coffin and the table with the hypnotic pattern.
the Lukas family - Weird ass family, described in MAG13 (funeral of Evan Lukas). Evan (got estranged from his family), Mordechai (associate of Robert Smirke), Nathaniel (founder of Solus Shipping PLC (The Tundra) and major investor in the Stratosphere Group (Daedalus)), Peter (Captain of the ship The Tundra).
The People's Church of the Divine Host - Cult founded by Maxwell Rayner, active around 1980's-90's and fragmented after Rayner disappeared. People associated: Linette Montauk and later Robert Montauk (serial killer, who's daughter Julia makes a statement in MAG9), Natalie Ennis (MAG25, the christian roommate who suddenly converted and kept unscrewing lightbulbs in the house)
The Lightless Flame - A cult, sometimes also referred to as Asag. People associated: Agnes Montague (grew up in the house on Hill Top Road, hanged herself at the same time when the tree in the backyard was cut down), Jude Perry (likes to light things on fire), Diego Molina (Gerry Keay kills him in the hospital in MAG12), Arthur Nolan (landlord of Jane Prentiss).
Not a character but also good to know:
The Magnus Institute - The Magnus Institute, London, is an institute dedicated to academic reseach into the isoteric and the paranormal. The building consists of the following departments: Artifact Storage; the Archives; the Library; the canteen; the tunnels below the Institute.
The Institute is built on the ruins of Millbank Prison, which was originally designed as an easy to navigate 'panopticon prison', with cells surrounding a central watchtower. This design was abandoned and eventually Robert Smirke made a design very similar, except that this one was a bit of a maze. It was built, but closed and demolished in 1890. The prison is gone, but the tunnels are still there below the Institute, accessible through trapdoors or by punching a hole in the wall.