This is a brief description of how initial spawn waves , types of aliens ( not including mutants ) , and behavior of aliens work.
SpawnThis only works for aliens spawning from the ground, while the marked spawn points retain fixed patterns. Aliens spawn-rising from the ground usually appear in clusters, mixed up with each other. They will usually spawn close to the player, at a considerable distance. The game will consider data like the amount of players at one spot and player experience. For example, two players camping with each other will experience two fold of the amount of aliens than the remaining player.
The route the aliens take to the player is determined by the environment around them. While an obstacle is between them, they are programmed to circle around the object in whatever direction possible to find a way over, under or around it. Their AI is powerful enough that they can navigate up ramps to reach the player.
These aliens are very simply programmed, their main objective is to charge at the closest player. When it reaches a distance close enough to the player, there will be a span of time given to the player to react before it attacks.
This enemy is much more intelligent than the regular Digger. While at the right distance, the panther will line up in a stance to execute a pounce attack on the player. This alien is much more agile, able to jump over obstacles and climb steep surfaces.
This alien has ranged capabilities. It keeps a distance from the player as it has no melee attack, while it shoots a barb at the player. The distance is always fixed and pre-calculated, as the barb goes in a fixed trajectory, the only variable being its position. This means that the Scorpion retains 100% accuracy, given that the player stays at one spot.
This is an airborne enemy with ranged capabilities. The altitude it keeps from the ground is fixed, as seen when it rises while navigating up ramps. It shoots a sphere of energy that looks like fire at the player, which also boasts 100% accuracy provided that the player is stationary.
This enemy behaves similarly to the Stalker, without its melee option. It has a shield that will negate 75% of your attack until it tries to attack you. During this stage the shield will deactivate, allowing for a brief moment of attack.
This is an enemy that has high attack and defense capabilities. When it spawns it will charge at you for a short amount of time. Then it will walk towards you until it reaches attacking distance, then damage you with its horns.
This is an enemy with ranged capabilities. It will move towards you until it reaches ranged distance, then launch a Plasma Bomb at you. This bomb has a splash radius and will deal a high amount of damage.
Similarly to the Digger, this alien attempts to crawl towards the closest player at a moderately high speed. It will explode if it touches any player, killing itself and dealing very large amounts of damage to the player who touched it. The explosion has almost no range, so it is possible to kill it with a melee weapon without taking any damage if you don't let it collide with your character's hitbox. Because it has no other attacks besides exploding, this alien will not stop moving across the map at any point until it reaches a player or is killed.