Alien Life Forms (Long War)

Much like in vanilla, aliens deploy in "pods", which are "activated" by seeing them. Unlike in vanilla, alien pods are frequently made up of several different types of aliens, such as a Thin Man leading some Sectoids, or some Mutons with Floater scout.

One alien in a pod will be a squad leader, with improved stats and sometimes new abilities. They can almost always be identified by their higher health than normal.

The aliens will continually improve their technology as the war goes on, which will grant them extra stats, HP regen and in some cases unlock new abilities, so the aliens in your individual game may differ a little than described below.

Sectoid

Sectoids behave in much the same way as you'd expect from vanilla, with low Mobility, HP, Aim, and Will. Basic Sectoids have access to a few more psionic powers than before, being able to Mind Merge, Mind Fray and Psi Panic. Their low Will means they won't be particularly effective at using these powers (Mind Fray will typically only do 1 damage for example). Be aware that Mind Merge has been altered so it does some damage to the merged target if the merger dies, but doesn't kill outright. Sectoid squad leaders get the Low Profile perk.

Drone

Drones will be encountered right from the beginning of the game, even in the first mission. They can come in groups of their own or attached to Sectoid squads, and later they will accompany more powerful mechanized units like Cyberdiscs and Sectopods. Drones behave similarly to vanilla, but, like most mechanized units, have some damage reduction. Their constant light cover from flying with damage reduction and ability to mutually repair can make them extremely frustrating to kill. Drones have Holo-Targeting, making them a bit more dangerous when supporting other aliens.

Outsider

Long War Outsiders are enormously more dangerous than vanilla Outsiders. They start with 9 HP and 3 HP regeneration per turn, meaning it will take a concerted effort from the whole squad to take them down early game. Like vanilla, Outsiders are mostly found in charge of UFOs, usually holed up on the bridge, but not always. You should be careful not to activate a UFO's Outsider until you're ready for it, since their HP regen means they can easily take on 1 or 2 XCOM soldiers without even taking damage. On larger UFOs Outsiders spawn in larger groups than in vanilla.

Thin Men

Thin Men are quite similar to vanilla, with high mobility, mediocre aim and low Will. The main change is that their poison has been replaced with Acid, which lowers aim and mobility as poison does, and affected units take slightly more damage from attacks, but acid no longer causes damage directly. Instead, acid inflicts damage to a victim as they take actions, so moving, reloading, firing, overwatch, etc will all cause an affected unit to take 1 damage (dashing will cause 2 damage). A unit that goes on overwatch will take the damage when they go on overwatch, not when they fire. Hunkering Down is safe and a unit that simply remains still and hunkered for the duration of acid will take no damage at all. Acid clouds dissipate within 2 turns and the acid debuff lasts 2-5 turns. Robotic units and soldiers with medikits or sealed armour are immune to the mobility effects of acid and won't take damage from actions, but will still take more damage from attacks and have reduced aim while affected by acid.

Floater

Floaters behave identically to vanilla floaters. Floater squad leaders gain the Damn Good Ground ability, which, given their ability to fly, makes them significantly more dangerous than regular floaters. Squad Leaders will have Close Combat Specialist.

Chryssalid

Chryssalids are similar to vanilla Chryssalids. A big difference is that Chryssalid squad leaders have Lightning Reflexes, which can seriously reduce the amount of damage a charging Chryssalid squad will take from overwatch fire if the squad leader moves first. Like Thin Men, the Chryssalid's claw poison has been replaced with acid.

Seeker

The Seeker

Seekers can be found both in pods made up entirely of Seekers, and accompanying squads of other aliens. This indirectly makes them more dangerous than vanilla, since a Seeker itself isn't much threat, but a Seeker supporting other aliens can be a deadly distraction. Seekers have had the shackles taken off their AI, and will happily decloak and strangle 4 of your soldiers at once. As mechanized units they have some damage reduction, which makes them difficult to damage with low power weapons like pistols and carbines. Note that Battle Scanners are available to any soldier as carried items in Long War, giving an early counter to Seekers. Seekers only cause 1 initial damage when strangling, but this damage doubles every turn they remain attached, so quickly knocking a Seeker off will result in minimal damage, but if left it will cause massive damage in 3-4 turns. However, they do now have the habit of going into Overwatch while in stealth. If you savescum, and a soldier has an AoE attack handy, you can use this to your advantage if you trigger this.

Muton

Mutons are similar to vanilla Mutons, and will start with Plasma Carbines and later upgrade to Plasma Rifles. Muton squad leaders have significantly more HP than regular Mutons, and have the Opportunist perk.

Cyberdisc

Cyberdisc - open assault form

Cyberdisc - closed disc form

Cyberdiscs are similar to vanilla Cyberdiscs. They get the Automated Threat Assessment perk, which given their habit of immediately going on overwatch when seen will often give them extra defense at least for the first turn. Cyberdiscs are usually accompanied by drones.

Mechtoid

The Mechtoid

Mechtoids behave identically to vanilla Mechtoids. Like vanilla, they will appear with Sectoid escorts, and later with Sectoid Commanders.

Berserker

Berserkers can also be Squad Leaders, meaning the first Berserkers you see could have terrifying amounts of health.

Since it's possible to have multiple soldiers with Rift outside of the Temple Ship, using their aggression against them to make them wander in and out of the psionic storm will make quick work of them, if you can set up the situation. With a few other AoE attacks, a cluster of them becomes a comedic slaughter: excellent payback for all the times they will crush your soldiers under their fists.