1) Alma - F.E.A.R Series.
Alma is the vengeful – and unfortunately, psychic – villainess of the F.E.A.R. series.
She manifests herself in three forms: Creepy girl in red dress, naked emaciated woman or healthy naked woman. All of those forms are bone-chilling when they appear in-game as Alma conjures up a storm of nightmarish images.
2) Pyramid Head - Silent Hill series
He resembles a pale, muscular man covered with a white, blood-soaked robe reminiscent of a butcher's smock. He does not speak, but grunts and moans painfully. His most outstanding feature is his large red, triangular head. His weapons consist of the deadly and heavy Great Knife.
3) Predator - Aliens vs Predator
The predators as a race are great hunters, with trophies from many species across the galaxy.
They often wear masks, and their faces resemble large crustaceans. Their equipment consists of invisibility technology, as well an array of weapons, including powerful shoulder cannons. They also wear small but powerful bombs on their wrists in case of defeat.
4) Tyrant - Resident Evil
The tyrant was a series of biologically engineered organisms created by the Umbrella Corporation to serve as potential supersoldiers. While most Tyrants in the Resident Evil series rely on sheer physical force to subdue opponents, Nemesis is able to use a shoulder-fired handheld rocket launcher.
5) Berserker - Gears of War
They have myopic vision, and as such they mostly rely on smell and sound to locate enemies. If anyone moves too quickly or makes other distinct noises (for example: firing a weapon), a Berserker will charge the source of the sound and attempt to either run it over or bludgeon it to death. If the sound is made while the target is behind a wall or any other solid object that the Berserker cannot break through, the Berserker will put her hand out in front of her and attempt to 'sniff out' her foe.
6) Scissorman - Clock Tower
He is a serial killer who is constantly in pursuit of the protagonist. His trademark weapon is a massive pair of scissors that he uses to stab and cut his victims. He sometimes becomes involved in a hide-and-seek type of chase with his victims. e seems to take some childish delight in playing with his victims before he kills them. It is heavily implied that he is a demon, as it is discovered that his mother Mary was a cultist, and in the opening cutscene the baby Bobby's eyes are completely white.
7) Nemesis - Resident Evil 3 : Nemesis
Nemesis is characterized by its relentlessness, strength, sheer stamina, and comparatively high intellect. Unlike the various Tyrant models before him, Nemesis shows it's capable of employing weaponry and firearms to achieve his objectives. He is also shown to have rational thinking abilities, as when he shot down a potential rescue helicopter and can even speak to some extent.
8) Sarah Kerrigan - Starcraft
She is described as a moral character, exemplified in her opposition to Arcturus Mengsk using the Zerg against the Confederacy. However, after her transformation by the Zerg, Kerrigan is freed from her inhibitions—as well as her neural conditioning—and indulges her darker traits. Her attitude is described as "spiteful, conniving, mocking, double-crossing [and] flamboyant", which when combined with her natural intelligence makes her extremely calculating and manipulative.
9) G-Man - Half Life Series
G-Man is a key, yet mysterious and enigmatic character in the Half Lifes series. Referred to as a "sinister interdimensional bureaucrat", he is known to display peculiar behavior and capabilities beyond that of a human and his identity and motives remain almost completely unexplained.
10) Shao Kahn - Mortal Kombat Series
Shao Kahn the Konqueror is represented as the embodiment of evil. In many respects, he resembles a large Asian warrior, and is well known amongst the roster of Mortal Kombat Kombatants for his godlike strength which rivals that of Raiden, the God of Thunder. He is also known for his extreme callousness, brutality, ferocity in battle, and his fondness of personal executions, though he has occasionally spared the lives of his subordinates, if they prove their worth, and his victims such as Sindel and Kitana, raising the latter like his own daughter and treating the former like his own wife. However, his true power that has served him well and allowed him to rise above the image of a mere warlord is his high intelligence and profound knowledge of the black arts.