By far, Alien: Isolation, with the Xenomorph XX121 aboard the Sevastopol spaceship.
What makes the Xenomorph so deadly, is the fact that the player can’t kill it and can only defend or hide from it, along with other systems and mechanics I will mention.
The Xenomorph AI relies on an interesting AI strategy achieved with a two-tier system consisting of a Macro AI and Micro AI. The Macro AI system or Director AI is always watching the status of the player, the Xenomorph and the environment.
While the Micro AI acts as a part of the Alien AI helping to guide the alien in where it should be looking for the player. However, the Xenomorph never knows the exact location of the player, but the director AI will guide the alien to explore areas near the current player with the help of any noise the player makes.
Also worth mentioning, is The Menace Gauge, part of the Director AI, which measures how much pressure the Alien is putting on the player. It also measures how far the Xenomorph is from the player and how many times the Xeno is within proximity. Once the menace gauge is at its maximum, the Director will send the Xeno to another part of the ship, giving the player a break from the pressure and time to progress through the game.
Now, there are also two main Alien AI states, which consist of an Active stage and the Passive stage. The active stage is where the alien will actively search an area in reaction to the player’s noise. The passive stage is where the alien will retreat to an air vent further ahead in an attempt to predict the player’s movement. That’s where we see the alien waiting for you above a vent to pounce on you.
The alien drool can be seen coming from the vent.
Now, what makes the Alien AI the best enemy AI, is its searching system, which has the Xenomorph search all prescribed locations in any given sequence, meaning it sometimes double checks an area to make sure the player’s not there or stop for a few seconds in one location. Given this unpredictability, the player never knows when or if the Xenomorph will appear.
The same system applies to the Working Joe androids.
