Apocalyptic Log: His video project, initially meant to be focusing on the twelve tribes of Israel, turns into this.
Ax Crazy: Seems to become this in the second part of "Thanksgiving Day Footage" under the influence of the Observer. Sarah finds him in a daze, covered in blood and wielding a knife. It is later revealed he in fact murdered Sarah's friend Kat.
Noah's cousin and close friend, Milo was haunted by the Slender Man during the time he visited Noah in 2008. He committed suicide in 2010, and Noah's inspection of the video recordings he made in 2008 reveal that the Slender Man may have had an influence in Milo's death.
Red Herring: It was implied he was the host for Firebrand. Turns out Firebrand is in fact a future or alternate version of Noah.
Weirdness Magnet: Let's see... mother was a member of a Slendy-worshipping cult? Check. Involved in a mysterious fire as a child? Check. Received treatment from Dr. Corenthal? Check. Followed by Slendy as an adult? Check. Targeted (and possibly driven to suicide) by the Collective? Check and mate.
Noah's friend (and YouTube follower) who invites him to stay with her during Thanksgiving break. However, the influence of the Collective follows, leading to Sarah becoming involved with the Noah's problems for a while.
A Day in the Limelight: In the Thanksgiving two-parter, she handles Noah's video camera and witnesses Noah's moment of madness.
Killed Off for Real: She is taken by Slender Man and later confirmed to have been killed when Noah finds her obituary.
Oh Crap: She calls Noah during his first livestream and reveals the Slender Man has been stalking her.
Real Life Writes the Plot: Bad blood between Adam Rosner and the actress who played Sarah led to delays in filming, and finally led him to re-write the final part of the Thanksgiving Day footage so her character doesn't appear on-camera.
Sarah's friend who appears in the Thanksgiving two-parter. She is murdered by a crazed Noah off-camera, and her death is made to look like a suicide.
Noah's grandfather on his mother's side. He is from Germany, and speaks little English. He reveals to Noah that he encountered the Slender Man in World War II, and possesses a journal and knife belonging to death Nazi Sebastian Kraus, which apparently is the last record of an unknown historic event involving the Slender Man.
Sanity Slippage: Possibly; Mary implied that he started out fairly sane and normal, only to forget his English and become more crazed and paranoid as time went on. Of course, given the strangeness surrounding the family (and the fact that Mary is a veryUnreliable Narrator), his behavior might have been completely justified.
Secret Keeper: Hides the journal and knife belonging to Sebastian Kraus.
Milo's mother, Mary is known to have had mental problems since she was a child. It is revealed she has known the Slender Man since she was a child, referring to him as "Mr. Slim". She was also knew Dr. Corenthal when he treated Milo as a child. Also a member of the Slender Man cult.
Chekhov's Gunman: Implied to be a lifelong candidate for the Collective, and is suspected of being Cursor's host.
Harassing Phone Call: Mary calls Noah out of the blue after he spent months trying to call her, explaining her past with the Slender Man and that Mr. Scars is going to kill her and for some reason she assumes Noah knows who he really is.
The Killer In Me: She is believed to have murdered her ex-husband who she may think is Mr. Scars.
A group of powerful proxies who do the Slender Man's dirty work. They each have their own assignments and seperate goals. The driving force of the plot involves them needing the journal of Karl Maxwell, as it is the last piece of the puzzle for their plans for Humanity. Tropes applying the Collective as a whole include:
And We Must Scream: It's been implied that joining the Collective is not a pleasant experience.
Chess Motifs: Each member is given a chess piece to symbolize their rank.
The Eldritch Abomination himself and Big Bad of the series. As usual, he is stalking children—and, in this case Milo and Noah—but takes a backseat to allow his minion, the Observer, to keep an eye on Noah. He often pops up to scare Noah, and possesses animated Combat Tentacles.
The main antagonist of the series, this mysterious and shadowy figure delights in manipulating Noah for his own purposes. He is recognizable by his distinctive thick glasses, long hair and malevolent grin. Beyond that, what he looks like is unknown, as he has only ever been seen in rotoscoping. He is later revealed to be possessing Noah's friend Kevin, who helped translate Karl's German after Noah's first visit to his grandfather.
Fighting From The Inside: Kevin seems to be doing this: on the back of the Observer's note from The Live Stream Incident, Noahs find a note in Kevin's handwriting begging him to kill him so the Collective can no longer use him as a vessel.
Firebrand is a member of the Collective who appeared in front of Noah on November 11th, and is recognized for his pinhole eyes and smile. He is called "The Stubborn." He stops the Observer from taking Noah on 11/11/12 and hijacked the video INTERCEPTION, revealing information about the journal. The Livestream Incident reveals that he is Noah, from either the future or a separate timeline.
Mr. Scars is seen with his hands covering a heavily scarred face. He is called "the one who kills Mary" and "The Burdened", and Mary Asher believed that Noah knew his identity. Noah has mentioned on Twitter that he has had a recurring nightmare about Mr. Scars, finding him vaguely familiar.
Affably Evil: Seems to hate his own scars (judging his behavior in a dream Noah had about him).
Implied even more in DEUS EX MACHINA when Firebrand reveals Mr. Scars will deliver Karl's journal to Noah.
A malevolent character who possessed Evan from the Everyman HYBRID crew, HABIT is an Ax Crazy creature who seems to hate the Slender Man. So much so that he frees Firebrand from the Slender Man's control and joins forces with him.