The Eyeball Monster is a minor monster that patrols the outside of Green Roof Apartments. While the main body is humanoid, its head is deformed. In place of any usual human features, its head is enlarged and covered in eyes. It also possess an extendable neck that can stretch as high as the 14th floor of the building. This monster does not appear to possess the same aggressive/cannibalistic instincts as other monsters, as it is content with just peering into people's windows. However, it will get aggressive if attacked. The monster can create a sharp-toothed mouth if attacked or if it needs to speak. After Dusik Hahn severed its head, the head shriveled up and died. However, the main body survived. It could not regenerate its head, and instead a bunch of small eyes were created in the exposed neck cavity.
Hyun Cha first spots the eye monster outside the apartment through his window, but he pays it no mind. The eye monster, later on, extends its neck to spy on Hyun, which greatly unnerves him. At some point, Hyuk Lee notices the monster as well, and talks to someone on an online game about it, not knowing that he is talking to Hyun. Later, as a father attempts to rappel down the side of the building to get supplies, the Eye Monster sneaks up behind him. When the father notices, the surprise causes him to lose his grip and fall to his death. The monster attempts to extend his neck into the children's room, but Hyun throws a keyboard at it and provokes it. Hyun then manages to stab it in the eye. Unfortunately, this did not kill the monster. Dusik ended up saving Hyun's life after shooting the monster with a homemade gun and severing its head from its neck. The main body survived and began walking away. Later the body is found in the forest in an incomplete cocoon, seeming to be unable to complete this form and dieing. It is unknown what happened to the monster since.