In no particular order-
1.Barnacles from Half-life
The barnacle creature attaches itself from the ceiling of a room or object and lowers it super adhesive tongue in the environment. As soon as you come in slight contact with the tongue the barnacle pulls you inwards and upwards by retracting it’s tongue in its mouth with you stuck on it. Then ,as you are suspended in mid air it chomps it teeth to severe your torso from the lower half of your body. Creepiest thing is that barnacles are positioned across chasms or rifts and seem like ropes on which you can jump on.BTW,if your’re caught by a Barnacle in-game,you are alive for a few seconds and stuck inside the Barnacle’s Body while you hear disgusting sound of Barnacle’s Digestive juices marinading your former Organs and a slight chomping of it’s formidable jaw.
2. The Flood from Halo
The flood’s infection form latches on to your Spinal cord to spread the infection and control the Host’s brain and motor functions.What’s scary is that the flood retain all the skills and memories of the host and get more intelligent and dangerous as there number increases and also they make a weird damp sound when approaching their prey,which just creeps me out.Also, you can get infected by the flood if you inhale any air which contains fragments or spores of the infection and the flood are capable of surviving millions of years without food.A single spore of a Flood Life form is capable of infecting thousands of other living organisms.Each Flood life form is controlled by a collective Consciousness called the “Hive Mind”.The Hive Mind operates the Flood as a Utopian Parasitic society where each individual strives for advancement of its species.The Hive Minds possess Beyond Genius level Intellect.
3. Headcrab from Half life
Headcrab digs it’s four pincers in your skull and latches on to your Face. From there it breaks your facial bones to access your brain stem and turn you into a zombie.Headcrabs are also used by “The Combine” as ammo for their artillery.They are launched in pods at hostile locations to ‘neutralize’ any non-compliant biological life.Headcrabs covert their victims into Puppet-esque Zombies whose Neural and motor functions are controlled by the “organism” which uses a human’s bi-pedal features to efficiently devour other living creatures.
Also,they are a shamelessly inspired from “Facehuggers” from Ridely Scott’s Alien.
4.The Revenant from Doom
The Revenant is more of a badass than scary. It’s basically a Skelton with a jetpack and a neurologically controlled rocket launcher. It’s kinda scary when it removes your player’s hand and beats you to death with it.Revenant’s Gaunt frame is contrasted by a heavy piece of Machinery ie It’s dual shoulder strapped Rocket launchers.With it’s frame dripped in fiery red of the deepest hells,The Revenant is an extremely Reverent foe to headshot in any video game.