You were a minion of the Entity, not Slenderman, but something entirely different. The thing that gained control over your mind was a being that existed between dimensions, belonging to neither the third nor forth dimensions.
The Entity possessed your body and took control over you mind whenever it wanted, whenever it needed bloodshed and suffering. Now was one of those times.
A group of people were running from you in the world the Entity had created for its own pleasure. Your job was to wound and offer the victims to the Entity by placing them onto hooks that stabbed into their shoulders. Each person had only three chances to get hooked before your master would kill and take them for itself. While you did your job, the people would have to start up generators to open a large door that led to the real world outside the Entity's.
You had gotten the other four survivors already, one on a hook ready to die and the others already taken. But one survivor was being especially annoying to you, he kept throwing pallets down to block your path to him and maneuvering around corners. You had gotten tired of it.
You decided to silently stalk after Jeff, not letting him see or hear you. Once he got the last generator, you sprinting at him while he ran to the exit. With a weapon in hand, you delivered a hard blow to his back to knock Jeff down before grabbing him by the hair and dragging him to the nearest hook to please your master.
A scream ruptured from Jeff's mouth as the full blade of the hook ripped through the flesh in his shoulder, holding him up by it while he was in excruciating pain. You stood and watched as he struggled on the hook, fighting back the entity.
If Jeff lost his focus for even a second, the entity would stab into his chest, back, and face before ripping him apart and bringing him into a cloud of dark smoke above the hook. It would kill and devour him in under a few moments if he made one wrong move.