Appearance

Body Features

The Slender Man's original abilities included:
selective invisibility (say, to adults or anyone without a camera)
the ability to change height and body shape
the ability to shape its arms into tentacles
and/or the ability to sprout tentacle-like appendages from its back and shoulders to be used as additional arms or legs (or simply to instill fear)

Special abilities

Powers and Abilities

The Slender Man has a highly varied arsenal of supernatural powers and abilities. He is immortal, having lived for at least eleven thousand years without end, and any wounds inflicted on him instantly heal.
Detrimental contaminants such as disease, pathogens, viruses, and bacteria are harmless to Slenderman, and he is also unaffected by poisons, toxins, venom, allergens, alcohol, drugs, and radiation. Slenderman also seems to be immune to fire. No work in the mythos has portrayed a definitive method of harming or defeating the Slenderman, and his victims usually survive by fleeing or psychologically conditioning themselves to ignore the Slenderman’s presence.
He can change and warp reality itself through various means, appearing to teleport matter. Although he sometimes crawls on his tendrils or far less commonly walks on his two legs, the Slender Man's primary means of movement is through teleportation – Slender Walking.[3]
This technique involves altering quantum mechanics, making him omnipresent until locked in one place when someone sees him.
Looking at the Slender Man causes negative effects, such as pain, disease, nausea, and technological disruption, although this is inconsistent and has led to the belief that the Slender Man can choose not to affect certain victims. He can also move himself and others through time. Slender Man can apply a deadly disease to victims known as the Slender Sickness. Effects include nosebleeds, nausea, amnesia, mental/emotional instability, diarrhea, vomiting, and constant pain. Slender Man's aura can also apply insomnia and the effects of contaminants like alcohol, drugs, and venom.[4]
Owing to his quantum and metaphysical nature, Slenderman can create limitless manifestations, avatars, and copies of itself across existence. This allows him to track down multiple victims at once, tormenting a single victim or a group of adjacent victims. He can also appear on other worlds, timelines, and periods. Slender Man can also manipulate his perceptibility, only visible in certain conditions or only appearing to certain individuals. His mere presence can alter the temperature to his likeness, and he can emit radiatio, usually Sigma radiation, for various effects.

Slender Man with his many tendrils.
Not even dreams are safe from the dark messiah, as Slender Man can freely enter and edit the dreams of others, as well as communicate with them telepathically. He can downright make victims his slaves through hypnosis, convince them of his goodwill through indoctrination and brainwashing, or make them do his bidding using mind control. He has shown the ability to adjust or wipe memories, controlling emotions and feelings, and create illusions, with physical illusions having the ability to interact with the real world, making others suffer hallucinations.
The mythos usually refers to victims under Slender Man's control or influence as Proxies. These usually receive special abilities by Slender Man, enhanced physical characteristics and a regenerative healing factor. However, a small group receives superpowers, like The Observer who was bestowed with the power to warp space-time, apply diseases, possess others and modify technology. Most Proxies can also cast illusions.
Slender Man can turn intangible to phase through surfaces. In addition to just his two arms, Slender Man can generate himself far more appendages: including more arms but also tentacles, tendrils, legs, and petiole. These appendages are exceptionally strong and can function as spears that can stab through reinforced metal. They can even crack space-time itself. The entity can freely change his body and change form, shape, and size.
He can flawlessly mimic voices as well as receive the abilities of anything he turns into, and the memories of any individual he turns into. Slender Man can also turn his into armor, and somehow even into a tree. A form the Slender Man has commonly used is a multi-armed skeleton.
In addition to himself, Slender Man can even transform others; he can turn people into the fog with but a gesture or mutate people or turn them into Proxies. Slender Man's primary offensive abilities include pyrokinesis (normal, green, and blue flames), and immunity to it, electrokinesis, umbrakinesis, and green explosive energy blasts, streams of which can flood a town.
Slender Man can create earthquakes and manipulate the weather, such as making it rain, snow, hail, or storm, and have lightning strike down or to conjure up gusts of wind. Slender Man can also use telekinesis to move objects with his mind alone and make others cough up blood. Using technopathy, Slender Man can take control of technology. He can also possess others. Slenderman's "helpful" abilities include prolonging death, reducing pain, resurrecting the dead, and applying morphine with his stare or a gesture.
More complicated abilities of Slender Man include space and time manipulation, the ability to alter time perception by shunting others through a private dimension, probability manipulation, causality manipulation, and the ability to create and modify custom worlds of his own, including mirror worlds.
Slender Man's single most powerful ability so far portrayed is to cause the Dimensional Bleeding – an event that leeches off universes and dimensions, distorting, disrupting, and potentially even destroying them.
The mythos has derived the above abilities from various works, sources, and authors – the fact that anyone can give their spin to the character makes Slender Man a highly inconsistent character. Authors may give Slender Man more abilities or leave powers out. It is overall extremely difficult to pinpoint a true, "canon" Slender Man. Therefore, the mythos uses a composite template for these abilities, drawing from various sources that fans cannot confirm nor debunk as part of the continuity.

Mentality

Education

Powers / Skills
Nigh-omnipotence
"Slenderwalking" (appearing and disappearing at will)
Teleportation
Extra tentacle-like appendages
Telepathy
Hyper-elasticity
Virokinesis (such as nausea and amnesia, commonly known as "Slender Sickness")
Shapeshifting
Impersonation
Memory wiping
Causing mental instability
Selective/conditional visibility
Invisibility
Intangibility
Quantum manipulation
Empathic manipulation
Hypnosis and mind control
Video and audio distortion
Pyrokinesis
Electrokinesis
Radiation manipulation
Regeneration
Death prolonging
Pain reduction
Day and night inducement
Morphine manipulation
Telekinesis
Thermokinesis
Possession
Resurrection
Technopathy
Somnipathy
Universe/dimension creation
Aura
Size alteration
Superhuman strength
Time manipulation and travel
Umbrakinesis
Hydrokinesis
Weather alteration
Essokinesis
Duplication
Geokinesis
Transfiguration
Energy projection
Acausality
Mind Manipulation
Probability manipulation
Incredible stealth
Mutation
Corruption
Claws
Immortality
Light manipulation
Transformation

Employment

Occupation
Tulpa (possibly)
Demon (possibly)
Interdimensional entity (possibly)
Stalker

Personality

Social

Contacts & Relations

Alias
Slender Man
Slenderman
Slender Beast
The Operator
The Administrator
The Entity
The Father
Thief of the Gods
Thief of Kuk
Him
The Skeleton
The Boogeyman
The Candlestick Man
The Man in the Fields
The Overseer
The Intruder
Tulpa
Der Großmann
The Thin Man
The Tall Man
Man
Der Schlanker Mann
Fear Dubh
Schlankwald
Tree Man
Slendy
Slender
The Pale Man
The Angel
Mr. Slim
Mr. Thin
The White King
The Faceless King
The Faceless One
The Giant
Master
Stick-in-the-Mud
The Keeper
The Monster
The Creature
X
Der Chirurg
Gorr' Rylaehotep
Windigo
The Ajax Monster
Black Shadow
The Virus
Black-and-White
The Knight
The Unknown
Daddy Slendy
The Suited Angel
Subject 87-Z

Aliases
Slender Person
Slender Being
ocheoteid

Family Ties

Alias
Slender Man
Slenderman
Slender Beast
The Operator
The Administrator
The Entity
The Father
Thief of the Gods
Thief of Kuk
Him
The Skeleton
The Boogeyman
The Candlestick Man
The Man in the Fields
The Overseer
The Intruder
Tulpa
Der Großmann
The Thin Man
The Tall Man
Man
Der Schlanker Mann
Fear Dubh
Schlankwald
Tree Man
Slendy
Slender
The Pale Man
The Angel
Mr. Slim
Mr. Thin
The White King
The Faceless King
The Faceless One
The Giant
Master
Stick-in-the-Mud
The Keeper
The Monster
The Creature
X
Der Chirurg
Gorr' Rylaehotep
Windigo
The Ajax Monster
Black Shadow
The Virus
Black-and-White
The Knight
The Unknown
Daddy Slendy
The Suited Angel
Subject 87-Z
Aliases
Slender Person
Slender Being ochroteid