Alien Life Forms (UFOAI)
As of version 2.5 the current alien life forms have been detected so far
Those are the most vulnerable among the aliens, not really fast nor tough to kill. They start wearing no armour and ramp up their protection while the game goes on.
Not really dangerous as they need to get into direct contact to harm your soldiers, but watch out for room corners! They are not made of flesh and blood so they cannot be stunned (not been able so far) to be recovered alive. Don't waste your ammunition on long shots: wait to get closer to them while standing outside their reach.
The advanced and more robust version of the bloodspider: they are the same thing but tougher to kill and dealing increasing damage.
These are really dangerous enemies. Being cybernetic (flesh and blood encased in a electro-mechanical device) they are immune to stun and gas with a high degree of hovering movement. Their favorite tactic is to shot from distance and they are quite accurate. Turn them down with your snipers as soon as you identify them!
As for the combat version of bloodspider, this version has a thicker armour and deals slightly higher damage.
These aliens are faster and stronger than the Tamans, but being made of flesh and blood they are subject to stun and gas and are not particular resistant to fire. They appear quite early in the game and scale up their equipment while the game goes on. They pose a greater threat than other races, both at distance and in close quarters, so turn them down beforehand.
Tough, tall and strong, members of this race are really dangerous enemies. They appear later in the game wearing powerful armours and weapons. They very often appear in heavy armour and due to their natural armour they can deal with one coilgun shot, requiring a second hit to be put on the ground. These are very dangerous enemies, you need to approach them in pack.