A lifeform that leaps onto human heads to infect and take over their bodies. It moves using four tentacle-like legs. Its speed is average, but it will pursue enemies until death. Its health is moderate. Once it takes over a body, the host attacks humans, grows sharp claws, and its blood turns dark red while the skin discolors. It growls and becomes more aggressive when provoked. The infection persists unless the main body is killed. A common mass-produced monster. It has a scarred, beige surface with bloodstains on its limbs. Its hind legs are short. Mostly small to medium-sized.

A lifeform that leaps onto human heads to infect and take over their bodies. It moves on four tentacle-like legs. While slow, it possesses high attack power and health. Once a body is taken over, it grows sharp claws and emits low, eerie growls while attacking humans. Additional Poison Headcrabs grow on the host's back and arms, using them to spread the infection. It is a stubborn, multiplying monster that must be killed at the source. Its surface is a mix of gray and beige, covered in stains and blood. It has multiple hairs on its legs. Mostly medium to large-sized.

A lifeform that leaps onto human heads to infect and take over their bodies. It moves on four tentacle-like legs at incredible speeds, allowing it to catch prey quickly. However, it has low health. Once a body is taken over, it grows sharp claws and gains immense speed to hunt humans, growling with every attack. The parasite must be destroyed to stop the infection. A powerful but rare monster. It has a black, rugged, and bumpy surface. Its legs are long and pointed. Sizes vary.

Residents of the city with various personalities. Many have already been infected by Headcrabs. This group includes soldiers. Only a few individuals retain their sense of self after infection.

Tasked with eliminating the Headcrabs. They are susceptible to infection themselves. They can be found throughout the city, always carrying firearms and prepared for combat. They wear helmets and tactical combat gear, and also carry grenades.