Strategies for Troops (Apocalypse)
Early in the game, it can be a beneficial tactic to set apart a few agents as a 'stun squad'. This squad carries stun grapples and stun grenades and is tasked solely with capturing aliens alive. Because they'll be getting up close and personal with brainsuckers, it's a good idea to comprise your stun squad out of androids.
Once you've got a few aliens stunned and down, keep your stun squad near them. Real-time makes this much easier, as you can set them for Aggressive and Auto-Fire and they'll automatically re-stun any aliens that try to stand up. Using a separate stun squad made up of three androids with twin stun grapples and grenades in a fresh game, this editor was able to capture alive an Anthropod, Spitter, Hyperworm, Multiworm, and Brainsucker all within two missions following acquisition of the Bio Transport Module.
Heavy Weapons and Real-Time Mode
Heavy weapons, such as the MarSec Heavy Launcher and the Dimension Missile launcher should be used with care in real-time mode. Personally, I recommend avoiding missile launchers entirely if possible, as one brainsucked agent in Disruptor armor with a dimension launcher can cause some serious pain later in the game's stages. Unfortunately, the game's AI doesn't seem to check friendly fire prior to using weapons, and you can easily end up destroying your entire squad if you don't keep heavy weapons reigned in. If you must use weapons like these, this editor recommends keeping all of your "heavy weapons experts" in the same squad, setting that squad to 'No Fire', and manually ordering them to fire when it's tactically sound to do so. An excellent example of this is when you're tasked with disabling parts of alien structures later in the game.
Marksmen, Sharpshooters and Snipers
No armed organization can go to war without its snipers, they provide accurate, long-range cover fire to your other squads and, if used correctly, serve as spotters for target acquisition to aid your other squads. The minute you start a game you should be on the look out for recruits with an accuracy skill above the rest of your troops. Try not to use Androids for this task as their accuracy is a fixed value and will never improve, Humans make the best long-term snipers. Make sure these are always participating in combat training to improve accuracy, among other things. Give these guys sniper rifles and keep them in a squad together. (don't forget to arm them with stun grenades and grapples) When possible buy the Marsec Body Armour Units as these have the built in jetpacks which allow your snipers to stay out of harms way and to take the tactical high ground quickly as well as provide dynamic support for your troops on the ground. Always place your snipers on high ground if possible, ideally 3-4 floors above your other troops. This gives them un-obstructed fields of fire and sight, something that your agents lives depend on. Snipers are there to support other squads and are best used in a ratio of 1:2 1 unit of snipers to 2 units of machine gunners. However, bear in mind snipers become less useful towards the later stages of the game but still has uses, especially in ufo recovery, set them to watch the door from the cliffs either side.
Early Game Strategy
The Super Scout Strategy (real-time only)
It can be useful to use a lone Android as a scout to uncover the map and find out where the enemy is. Use the unit with the highest speed and strength if possible so that it can carry a lot of gear and also get away from the enemy as needed. Android immunity to brainsuckers is particularly useful here should you wind unexpectedly at close quarters. Sending a lone soldier gives your two particular advantages: he is easier to micromanage and maneuver and you're only risking one soldier. This also brings a new dimension to the game, as you can fight a large portion of your battles in solo mode if you are careful.
Armed with a sniper rifle, lawpistols, two Stun Grapples and a motion scanner, you'll have a mixed bag of weaponry for engaging at any range. It's particularly fun to harass the enemy with sniper fire and grenades, and retreat if there are too many. You can also liberally sprinkle the battlefield with stun gas grenades to keep the enemy off-balance or when you want to capture aliens alive. Also, gas grenades are safer to use around civilians or your own squad members. This brings up the next fun part--leading the aliens into an ambush. Support your android with a small squad of three solider equipped with long and short range weaponry so that they'll be ready for any sort of encounter. In addition to providing extra firepower, your allies can keep an eye on any unconscious aliens should they wake up.
As for what other troops to bring, it's up to you. I like to bring along a dedicated group of four snipers and four machine gunners to cover the flanks and establish a safe perimeter to retreat too if necessary. They can also act a reserve force if you get into trouble, though most of the time, they just sit at the edge of the map and take potshots at enemy which helps train their accuracy. Let them waste Lawpistol or Auto Cannon ammo if you find yourself burning too much machine gun ammo, which always seems to be scarce.
It's also useful to note the lawpistols are surprisingly useful when paired with a sniper rifle for your mixed troops since they are light and compact and offer comparable firepower to the machine gun without the weight. They can also be dual-wielded without accuracy penalties, which is another plus. Of course later on, they will be replaced by plasma guns, assuming there is enough ammo available.
Lastly, your scout should have a motion sensor. It's also handy to give one to the leaders of all your other squads so they enemy will not get the jump on you. You don't *have* to give the sensor to the leader, but this really helps cut down on the micromanagement, which seems to the be most tiresome part of battles.
Late Game Strategy
"Stealing" Personal Shields
Late Game, Personal Shields are rather ridiculously useful, since they will absorb almost any form of damage from enemies, and they absorb a LOT of it. Plus, they recharge over time. The only reason not to outfit everyone in your squad with multiple shields is that they take a lot of time to manufacture. So, the simplest way to get lots of them is to get them from the aliens OR on raids against humans. Only humanoid aliens can carry personal shields, and there's a limited amount of aliens compared to being able to raid the COS ad infinitum. So, the best way to get lots of shields is via raiding the COS.
Now, when you raid the COS for shields, you want them to either drop their shields units or you want to do damage that bypasses the shields. Shooting normal projectiles to wear down the shields will result in the shield units being destroyed instead. Therefore, you want to bring along PSI troops to make the COS drop their items before you kill them. Simple enough, if you've trained up strong Psi troops.
The other method of obtaining the shields is to use either Stun Grenades or Toxiguns. Stun Grenades will make them drop their items when they fall unconscious, but are a little harder to use. A simpler way to get shields from COS is to play in Turn Based mode and to shoot COS from point blank with your Toxigun on full auto. Please use Toxin A or basically your weakest Toxins, since human targets are unaffected by the poisons of the Toxigun and seem to only take damage equivalent to a machinegun shot from each shot fired regardless of Toxin type used. Most COS will die in about a dozen shots, so at minimum, you need around 15 TU once you're right next to them for the kill. But, you should only be doing this for COS targets that are carrying shields. Therefore, you should carry a Devastator/Disrupter in one hand and a toxigun in the other. Get to point blank range and fire a Disrupter shot into the target. If you hear a dull thunk and see the blue shield flash, switch to the toxigun and pepper him full of holes. If you hear a scream, kill him with the disrupter. Or you can just scan the enemy with the mind bender. Note also that enemies will seem to be able to only be carrying ONE of the following: Personal Shield, Teleporter, Personal Cloaking Field. So, if you see a fuzzy looking unit, just Disrupter him to death, he won't be carrying a personal shield.