The Core (Hallucination)
Creepers are leaner than most Zombies, skinny to an almost skeletal design. Their fingers are long, claw-like appendages which they use to tear apart their prey. Their skin is a pale gray, almost identical to the color of bone. Their entire head is made up a Venus Fly Trap-like structure, the lining of the mouth aligned with sharp teeth with wide gaps between each one.
Creepers use the same, if not modified scripting as the Fast Zombie in Half-Life 2. They are leaner and skinnier than their zombie counter-parts, allowing them to run, leap at, and attack targets with astounding speed. Though they are less dangerous individually due to the minor damage they inflict, they can prove to be quite a nuisance in packs. They are relentless in pursuing their targets, not stopping until they or the victim dies. After executing the two-handed slash, they stop to let out a hissing screech at their targets. The reasons for this are unknown, though it could simply be an effort to scare the prey.
The Creeper is first introduced in the chapter Maintenance, where it runs past the Patient towards the direction of the laundry room. In "Operation", the Creeper once again runs past the Patient. Right before meeting the SWAT Team, the Patient undergoes a dream sequence where he is in a dark, bloody place with pillars, and Creepers are seen running past him in various directions. For a while, the Creeper is nothing more than a passive creature. However, after Johnson disappears, the creatures begin to attack the Patient directly.
The Patient and the SWAT Team are assaulted by a horde of Creepers in the hospital's warehouse. In the final chapter, they serve as a part of the final boss, defending the Core from destruction. They are confronted in the first hallucination while fighting the Core that Dr. Romero traps the Patient in, with him rendered helpless while they charge in numerous numbers. However, all of them are simultaneously killed by Emily Romero before they can reach him.
Though they can prove to be a nuisance, Creepers are relatively not a dangerous threat on their own. It is possible to instantly kill them with the .357 Magnum or Shotgun once they are close enough to you. It is possible to predict when they lunge at you and evade them, allowing for an easy counter-attack. When facing multiple zombies, it is best to use the SMG, as it is capable of taking them down moderately quickly.
Creeper has a Photo Gallery.