%%
%% ZeroContextExample entries are not allowed on wiki pages. All such entries have been commented out. Add context to the entries before uncommenting them.
%%
[[quoteright:300:http://static.tvtropes.org/pmwiki/pub/images/x_geoscape.jpg]]
[[caption-width-right:300:''Vigilo Confido.''[[note]]We Are Watchful, We Are Necessary.[[/note]]]]

The brainchild of Julian Gollop and other assorted Creator/{{MicroProse}} personnel, '''''X-Com''''' is a European series of TurnBasedStrategy games created in 1993. Players are put in charge of X-Com, a planetary defense agency, and tasked with maintaining X-COM's budget and catching {{flying saucer}}s (either by storming their landing sites or shooting them down). Most of the games operate as a hybrid of [[TacticalTurnBased turn-based tactics]] and [[ResourcesManagementGameplay resource management.]] The games have a fair amount of [[RandomNumberGenerator randomness]], although the better player will tend to win.

The first title, ''UFO: Enemy Unknown'' (marketed as ''X-COM: UFO Defense'' in North America) was a watershed title for the genre which is still hailed as one of the best strategy games ever. Despite its modest origins, the ''X-COM'' legacy was not a solo act: While Gollop's team set to work on a sequel called ''X-COM: Apocalypse'', an in-house crew at [=MicroProse=] beat him to the punch in 1995 with a MissionPackSequel: ''X-COM: Terror from the Deep'', which is set 40 years after the First Alien War.

''Apocalypse'' was released in 1997 to average reception, and included the option to play in [[RealTimeStrategy real-time]]. The last days of [=MicroProse=] (and its acquisition by Hasbro Interactive) saw ''X-COM'' have two {{Genre Shift}}ed offerings: ''X-COM: Interceptor'' (1998), an {{interquel}} which kept the base management elements while swapping out the strategy missions for space-bound [[SpaceFighter flight sim]], and '''''X-COM: Enforcer''''' (2001), a GaidenGame which ditched the strategy part outright in favor of a FirstPersonShooter.

After that, the possibility of a future ''X-COM'' game became uncertain due to the rights passing between various companies. In 2010, [=2K Marin=] announced that they were developing a ContinuityReboot of the series: an FPS set exclusively in the USA in TheFifties. The fandom's negative response to the reboot was heavy enough that, instead, Firaxis Games (a subsidiary of 2K and developers of the ''VideoGame/{{Civilization}}'' series) was tasked with creating a new game closer in-line with the original ''X-COM''. The result was ''VideoGame/XCOMEnemyUnknown''. The original FPS reboot was {{Re Tool}}ed into a [[ThirdPersonShooter third-person]] tactical shooter called ''VideoGame/TheBureauXCOMDeclassified'', intended as a prequel to ''Enemy Unknown'' (the game's three separate iterations [[http://www.ign.com/videos/2013/05/10/the-evolution-of-the-bureau-xcom-declassified are documented here]]). In 2015, it was announced that Firaxis was working on a sequel to ''Enemy Unknown'', named ''VideoGame/XCOM2'', exploring X-COM as a underground resistance group, fighting against the alien occupation forces and the VichyEarth government.

As of late March, 2016, the three games of the classic series (along with ''Enforcer'' and ''Interceptor'') are available at [[https://www.gog.com/game/xcom_ufo_defense GOG.com]] (link goes to the first game).

!!Entries in the franchise:
* Creator/MicroProse continuity:
** ''UFO: Enemy Unknown'', released as ''VideoGame/XComUFODefense'' in North America (1994)
** ''VideoGame/XcomTerrorFromTheDeep'' (1995)
** ''X-COM: Apocalypse'' (1997)
** ''X-COM: Interceptor'' (1998)
* Creator/{{Hasbro}} continuity:
** ''X-COM: First Alien Invasion'' (1999)
** ''X-COM: Enforcer'' (2001)
* Creator/FiraxisGames continuity:
** ''VideoGame/XCOMEnemyUnknown'' (2012)
*** ''XCOM: Enemy Within'' ExpansionPack (2013)
** ''VideoGame/TheBureauXCOMDeclassified'', {{prequel}} to ''Enemy Unknown'' developed by 2K Marin (2013)
** ''VideoGame/XCOM2'' (2016)

!!{{Spiritual successor}}s and {{fan game}}s
The earliest games spawned a number of mods and remake attempts. Various [[SpiritualSuccessor Spiritual Successors]] also emerged, such as ''[[VideoGame/UFOAfterblank UFO: Aftermath]]'' and its sequels ''Aftershock'' and ''Afterlight''. Another, ''Rebelstar: Tactical Command'', came out on the GameBoyAdvance along with ''Laser Squad: Nemesis'' (in and of itself a sequel to ''X-COM'''s own predecessor ''Laser Squad'') and ''[[http://ufo.ufo-extraterrestrials.com/ UFO: Extraterrestrials]]'' which is almost an exact remake of the original game.

Fans have also made their own remakes, most notably ''[[http://openxcom.org/ OpenXcom,]]'' ''UFOAlienInvasion'' and ''VideoGame/{{Xenonauts}}''. [=OpenXcom=] itself has enabled total conversions like the ''Xeno Operations'' and ''VideoGame/{{Piratez}}'' mods.

-----
!!The ''X-COM'' series provides examples of:

[[folder:General]]
* ATeamFiring: ''Grumble...'' Most recruits will hit [[http://static.tvtropes.org/pmwiki/pub/images/AW-XCOMAccuracy.jpg everything except the aliens.]]
** This is less the rookies' fault as it your weapons. This is especially evident when using Auto Fire (which makes soldiers shoot 3 less-accurate shots in rapid succession). Agents can even be firing an ''accurate'' weapon like any of the Rifles at point-blank on full auto and have the shots knock down the walls and trees behind an alien without even grazing it. Aimed Shot (a single, more-accurate shot that eats up more of your Time Units for the turn) is practically a necessity for any enemy who isn't in point-blank range. On the other hand, Plasma weapons are vastly more accurate than ballistics or lasers; with those in place, even an auto-shot will prove effective with enough training in Firing Accuracy.
** Auto shot is preferable early on when you know even the soldier's aimed shot will most likely miss. First, it has a chance to hit aliens multiple times, stray bullets will sometimes hit other aliens (even those you didn't notice), and if the alien can see you, a single burst will only trigger reaction fire once as opposed to aimed or snap shot which trigger reaction on every shot. Even if you only have a 20% hit chance, in a burst of three it means 48.8% chance that at least one will hit. Once you have laser weapons, you most likely use auto shot at every opportunity.
** Snap Shots, on the other hand, are only useful if you're standing '''nose-to-nose''' with an unarmored alien; otherwise you hit air. You're better off spending your [=TUs=] on 1-2 Auto-Shots than flushing them down the toilet on a Snap Shot. Waving your gun around like a lunatic and blindly spraying bullets into the air is preferable, literally, to carefully kneeling and firing off a Snap Shot.
** [[http://www.ufopaedia.org/index.php?title=Firing_Accuracy_Testing Experimentation]] has shown a few oddities with accuracy in the first two games. In particular, the quoted % accuracy is actually understated a majority of the time. The reason for this is that a "miss" is not actually a miss, but rather a random deviation applied to the bullet. If you're lucky (or at point blank range), this deviation will be small enough that the bullet hits anyway.
* AdventureFriendlyWorld: See CrapsackWorld. This works out fine as the backstory of a hyper-lethal squad combat game: the utter monstrosity of your enemy means that as long as any humans survive, the NonEntityGeneral can always find vengeance-crazed replacements for troops lost in combat, or at least someone willing to die for a carrot, and there is an unending supply of alien baddies to kill, capture and vivisect. But taken out of context, X-COM is essentially sending unaccountable death squads against an enemy that can never really be beaten without desperate measures.
* AirborneMook: The Floaters, their equivalents in the sequels, and various terror monsters.
* AlienAutopsy: The player's scientists can perform these to learn more about the enemy.
* AliensAreBastards
** The first two games played straight.
** Would have been subverted with the canceled ''Alliance'', where the stranded X-COM team form an alliance with the friendly aliens against the hostile ones.
** Downplayed with in ''Apocalypse''. The new aliens are certainly bastards, but some of the ones we've been previously familiar with now co-exist peacefully with humans.
** And then subverted again in the reboot: [[spoiler:Turns out the Ethereals are [[WellIntentionedExtremist Well-Intentioned Extremists]]]].
* AlienBlood
** Green and Yellow seems to be most common ones.
** Ethereals have silver blood (though it's dark red in its Autopsy picture).
** Aquatoid blood is orange.
** Lobsterman blood is teal.
* AlienInvasion: Though alien threat comes from a new source--space, underwater, and another dimension respectively.
* AliensAndMonsters: Mostly aliens, but their Terror Units are often engineered (genetically or otherwise) to either capitalize on their owner's strengths (Chryssalids having weaponized the Snakemen's rapid asexual reproduction, for example) or cover their weaknesses (Sectopods distracting the enemy with conventional attacks while their Ethereal masters make with the MindRape). Except for the [[GoldfishPoopGang Silacoids and Celatids]], which (given that their counterparts, the Mutons, don't really ''have'' weaknesses) don't really do anything.
* AllDesertsHaveCacti: Any desert you visit in ''UFO Defense'' has Cacti. Even the deep Sahara or the Rub al Khali. Even the desert in ''Enforcer'' has cacti.
* AllYourBaseAreBelongToUs: A major gameplay element; you have to design your hidden underground bases with defense in mind, since aliens ''will'' eventually find and attack them. Later in the game, of course, you get to do the same to them. (Or earlier, since unless you're doing a really bad job, you'll find some alien bases before they find yours.) Innovations in technology will eventually provides missile and psychic defenses to fend off [=UFOs=] or, in the case of the latter, cloud detection of the base completely. The Skyranger isn't exactly a safe haven either, both on the ground or in the air.
* AllianceMeter: ''UFO'' and ''TFTD'' has this in form of Funding Nations. Scaled up in ''Apocalypse'' with 25 factions waging corporate wars for political and economical power in Mega-Primus during the alien invasion.
* AmericaSavesTheDay: Your biggest financial contributor in ''UFO/TFTD''. Geographically, it's one of the most difficult regions to defend (the most difficult being Australasia) while still keeping a radar umbrella over the other donors, separated as they are between two vast oceans. Not a good site for a starter base; keeping a close watch on it with Skyrangers until you can afford a secondary base is the best way to go.
* AndYourRewardIsClothes: Each difficulty level you beat in ''Enforcer'' (in single play) unlocks a few new skins for the title robot.
* ApocalypseHow:
** The result of failing to defeat the aliens (and sometimes even when succeeding). See the more detailed AP examples in each games respective sections.
** ''Interceptor'': If you fail, the alien superweapon utterly obliterates Earth, leaving a smoldering husk behind. You get to turn the tables on them, though, [[spoiler:using the Nova Bomb to cause a supernova in their pocket dimension solar system]]. Technically, you can do it ''as much as you want'', which is a little frightening.
* AppropriatedTitle: The series started as ''UFO: Enemy Unknown''. It had to relabel itself ''X-COM'' when somebody complained there's already a game called ''UFO''.
* ArmchairMilitary: The "rear commander" tactic. Since high-ranking officers contribute to the Morale level (and significantly hamper morale when they get themselves killed), it will behoove you leave them behind in the Skyranger. The officer will continue to gain EXP and receive promotions, with the rookies and squaddies stuck doing all of the legwork. Once you go into psionics they can still make themselves useful, either mind-raping aliens or (if they're to weak psychically) scanning them with the Mind Probe.
* ArmorIsUseless: Armor won't be much use to somebody who just got shot right in the sphincter, either from behind or one floor below. Fortunately, this holds true for the aliens and mechs, as well.
** A soldier with maximum health and the best armor can still be killed in one shot if the damage roll is high enough. Even the best armour has at best a 50/50 chance of stopping a Heavy Plasma shot, though it does make troopers immune to many human weapons and it provides much better protection than most alien units have. To clarify, X-COM soldiers take 0 to 200% of the listed damage from firearms; 50 to 150% from explosives. Unarmoured troopers can survive several heavy plasma blasts and take absolutely no damage... only to be offed by a single pistol shot the next turn.
** The manual does state that the default coveralls ''do'' offer excellent protection from modern weapons, although it skimps over the plasma resistance capability...
** ZigZagged in ''Terror'': The front of the Ion Armor can let soldiers take point blank Sonic Cannon blasts or Lobstermen's claws and take no damage as long as it hits the front armor (unless random chance screws you over), but still played straight with Bio Drone explosions and Tentaculats. Also, Ion Armor is much weaker at the sides, meaning the alien waiting around the corner can easily take out your soldier if you're not careful.
** Averted in ''Apocalypse''. Megapol Armour is fairly competent, particularly against light friendly fire and early disruptor weapons, but is terrible against devastators. Marsec's flying armour is weaker but allows flight. On the other hand, X-COM manufactured "Disruptor Armour" transforms soldiers into [[TheJuggernaut nigh-unstoppable]] death machines who can practically ''waltz'' through multiple explosions without even taking a mortal injury. The shields certainly help, though.
* AttackDrone
** Cyberdiscs and Bio-Drones.
** ''Enforcer'''s protagonist. Recursively, he too can get an AttackDrone.
* AwesomeButImpractical:
** Several weapons and base components, either due to how easily their replacements can be researched or by being {{Nerf}}ed by the game mechanics.
** The Sonic Cannon of ''TFTD'' is the biggest offender. It can firing snap shots or aimed shots and inflicts about 15% more damage than the Sonic Blasta-Rifle. However, firing a snap shot will take ''half'' of your time units, and an aimed shot requires ''75%'', meaning you have almost no ability to manuever. In addition, it has five fewer rounds per clip, and is so heavy you're limited in what else you can carry. The Blasta-Rifle is superior in every way ''except'' damage and, to much a lesser extent, accuracy, but since you can fire two snap shots ''and'' move with the Rifle, the slight damage increase the Cannon offers is negligible. Fortunately, [[ArtificialStupidity the computer will use the Cannon, and all it's attendant problems, exclusively about two-thirds of the way into the game.]]
** The Griffon Tank in Apocalypse: Huge, has a BFG. Awesome stats for something you can get at the start... but because of a coding decision, will be destroyed if the road under it gets damaged, no matter what its current health is. Also, it's SLOW; flying vehicles can easily avoid it.
** Heavy infantry-carried weapons, at least in the first two games -- launchers such as the Auto-Cannon can inflict serious amounts of damage, but their weight means rookies will have problems carrying them. In general, equipping rocket launchers, auto-cannons and the like to inexperienced soldiers (which are all you've got in the early-game!) will mean they may not have enough [=TUs=] to actually fire them effectively or, not to mention, ''move''. The Blaster Launcher is the main exception and a [[GameBreaker/XCom Game Breaker]].
** ''Interceptor:'' The [[http://www.youtube.com/watch?v=z655q7pClO8 cutscene]] when you complete research on the Nova Bomb, which of course includes a test. The pilot who reports that the test was successful doesn't sound too happy about it. [[SlasherSmile But the player's avatar is.]]
* AwesomePersonnelCarrier[=/=]CoolPlane
** The Skyranger VTOL jet.
** ''Terror from the Deep'' introduces the Triton, a submarine equivalent of the Skyranger.
** The ultimate troop transports (the Avenger, Leviathan, and Annihilator) are also the ultimate fighter craft!
* BackStab: The Rear section is one of the weakest parts of wearable Armor, naturally leading to this.
* BeePeople: The Sectoids and Aquatoids are described as such. The ''Apocalypse'' aliens as well.
* {{BFG}}: The series is full of them, from the Heavy Cannon to the Rocket Launcher to the Heavy Plasma to the Blaster Launchers and their counterparts.
* BizarreAlienBiology: Autopsy results. Some are fairly mundane, some are heavily cybernized, and some who by all means should have been dead when they were alive.
* BlackBox: Even when research is done, there are still something that bugs the scientists, usually the autopsies of the more exotic aliens and miscellaneous tech. They sensibly ignore it rather than taking the (extra) time to figure it out.
* BlackMarket: Though not explicitly stated in the games themselves, the manuals say that X-COM sold goods to buyers of questionable reputation, and when the times became rough they even stopped bothering asking about who's buying as long as they had the cash.
* BodyHorror: Chryssalids, Bio-Drones, Tentaculats, several of the ''Apocalypse'' aliens, and so forth.
* BoringButPractical: Laser pistols and rifles, which are cheap to manufacture, fairly accurate and use up no ammunition. Thanks to decent rate of fire and damage, they remain useful for entire length of game, with sole exception being Mutons. You will later find yourself dusting off your old Heavy Lasers once Sectopods come out to play.
* BossRush: Completing ''Enforcer'' on Xtra Spicy grants access to the [=XtraSpicy=] bonus level, where each boss in the game attacks in pairs (at the minimum).
* BottomlessMagazines
** Only for laser weapons in the first game, the major reason they are so good. Hideously averted for everything else (see EasyLogistics below) except for aircraft and [=HWP=] energy weapons and even those just have very large magazines (100 or 255).
** While the first game went with the "more powerful weapon = more ammo in clip" method (the plasma pistol has 15 rounds, while the heavy plasma has 35), ''TFTD'' decided that more powerful weapons need smaller clips (the Sonic Pistol has 20 rounds, the Sonic Cannon has ''10'').
* BrainInAJar: The final opponent of ''Enemy Unknown'', later miniaturized into an enemy unit in ''TFTD''.
* {{Brainwashed}}: The common state of victims of Ethereals, high-ranking Sectoids, and their successors. Often, they're [[BrainwashedAndCrazy also crazy]].
* BulletholeDoor: Great for reducing the effects of drone blockage during Terror Missions. Busting through the walls of [=UFOs=], however, will take well-placed/lucky plasma holes (interior) or Blaster Launcher shots (exterior). Or [[BigBulkyBomb lots of plastic explosives]], but that's [[ThereWasADoor another trope entirely]].
* CharacterLevel: The Soldier ranks are a lesser example of this, and which soldiers get promoted is out of the player's control (though ''[=OpenXcom=]'' has a mod for manual promoting) based on the performance of the soldiers and how many of them are in your employ. The higher the rank, the better the morale the soldiers have. Getting the high ranking officer killed will also make the morale drop like a rock.
* CharlesAtlasSuperpower
** With sufficient combat experience, a soldier can eventually beat out a tank in health, movement, accuracy, etc. Oh, and tanks can't get those nifty Psi abilities.
** [=XCOMUtil's=] modified [=HWPs=], on the other hand, are absolutely terrifying, and are capable of reliably hitting an enemy from a considerable distance away. And if they miss, well, that's why you use the Rocket Tanks... until you get the Fusion Ball Tanks. Which can never miss, unless you're bad at setting in the missile course.
** Also demonstrated by Commander units on the enemy forces, particularly in ''X-COM'' and ''TFTD''. Your average Floater, for example, dies if you so much as glare at it. Floater Commanders can take several rifle rounds to bring down, on the other hand. Rank distinctions were removed in ''Apocalypse'', however, though enemy stats could vary greatly.
* ChestBurster: Chryssalids and Tentaculats.
* CloneArmy: Alien autopsies reveal that, with few exceptions, most of the aliens are clones.
* LesCollaborateurs: Repeated screwups in a particular funding nation or outright political manipulation thereof by the aliens can result in said nation cutting its remaining funding to X-COM and signing a nonaggression pact with the grey bastards. Most annoyingly, when you spot a UFO or USO on a "diplomatic mission", if they've landed, you're already too late. You can assault the aliens, kill every single one, loot their ship and prevent any further incursions into that particular nation's airspace, and at the end of the month be told that they've signed a non-aggression pact with the aliens. Even if the ship was only on the ground for five minutes.
* ColonizedSolarSystem: Mars is alien HQ in ''UFO'', colonized by humans after ''TFTD'' and is humanity's main source of elerium-115.
* ColonelBadass: The Commanders of both sides, though the actual rank of Colonel is the second highest. ''TFTD'' has the Captain and Commander as the highest and second highest ranks respectively.
* CombatMedic: Anyone with the medkit, and boy, you're gonna need them. You can also pick up a downed soldier's own medkit and use it on him, as knocked-out soldiers will instantly drop all their equipment on the ground.
* ConcealmentEqualsCover: Since all objects can stop at least one shot. Shame aliens tend to fire on full auto.
* CoolStarship: Completing a game often requires research and construction of an "Ultimate Craft" and interrogation for the whereabouts of an alien stronghold to drive it to.
* CowTools: Aliens bases and some ships are filled with these. Some you can research, some just look appropriate.
* CrapsackWorld: [[http://forums.steampowered.com/forums/showthread.php?p=31876257 All but stated.]] An unknown, but likely large portion of the galaxy is ruled by an AlwaysChaoticEvil HiveMind. Humans ''might'' be able to destroy the local node if they become TheUnfettered -- abolish every civil liberty and article of war. And there's another, unattached (albeit slightly less advanced) node in the Gulf of Mexico. And its destruction would reduce Earth's biosphere to the algae level. And there's an entire ''planet'' of Hive Mind aliens just one dimension over. And the best weapon against all these irredeemably hostile aliens are {{Half Human Hybrid}}s with PsychicPowers... who will eventually become a permanent underclass treated like parolees from cradle to grave and not allowed to breed without permission(which tends to be withheld between invasions). In short, not only is TheVerse irrefutably hostile, but it runs on FromBadToWorse.
* CriticalEncumbranceFailure: Of the "carry items up to the soldier's Strength in weight, then take Time Unit and Stamina penalties for going overboard" type.
* CriticalExistenceFailure
** {{Averted|Trope}} with soldiers. Those lucky enough to survive alien gunfire (and that won't be many of the unarmored ones, mind you) will leak HP from "Fatal Wounds" to their various body parts until they fall unconscious and are either treated with a Medi-Kit or left to die. More often than not, it's the latter. Wounded troopers also suffer an accuracy penalty.
** Played straight with Cyberdisks. Due to how 2x2 monsters work, a stunned cyberdisk is effectively a dead cyberdisk. Actually killing it results in a [[MadeOfExplodium rather impressive boom]]. Which can also cause chain reactions, if other cyberdisks are close enough.
** Played straight in ''Terror from the Deep'' with Bio-Drones.
* CrouchAndProne: In ''UFO'' and ''TFTD'' Soldiers can crouch to improve accuracy, become a smaller target, have more cover and to allow the standing soldiers behind the crouching ones to shoot over their shoulders (though be careful, there's still a risk of hitting the guy in front of you). Soldiers automatically stand up straight when moving. ''Apocalypse'' also has a prone position.
* {{Cyborg}} / BioAugmentation: Most of the alien mooks are modified one way or another.
* DamageOverTime: Most attacks have a chance to cause wounds that will bleed the victim to death if left alone.
* DeathFromAbove:
** The Floaters and their equivalents.
** Players can also do this once they research a means of flying.
** Some Enforcer enemies will do this. In particular one floating buzz-saw thing likes to reach you and flip up to where you can't possibly get an angle on it, attacking all the while.
** The best way to use the Blaster Launcher and its cousins is typically to have the round rise to the top level of the battlescape, where it will not be obstructed, navigate to the target, and then dive straight down on top of whatever hapless alien you're blowing away. This ensures a detonation; if it doesn't hit the alien, it'll hit the ground.
* DecapitatedArmy: In most games killing the alien leader and destroying the main base he was in makes you a winner.
** One tactic for assaulting larger alien craft that have landed or been shot down involves blowing a hole to the bridge and killing the alien officers ''first''. The remaining aliens tend to panic after a few turns and drop their weapons.
** The same is unfortunately true of X-Com's forces. If the highest-ranking officer is killed, the lower ranks suffer a major morale penalty. One reason why experienced players tend to leave the Commander inside or near the dropship, where he can launch Blaster Bombs at the enemy bridge (see above).
* {{Deconstruction}}: Of children's cartoon series such as ''Franchise/GIJoe'' and ''Franchise/{{Transformers}}''. ''X-COM'' is a team of elite soldiers who wear cool-looking armor and have a fancy CoolShip that they travel the world in to save the world from goofy-looking aliens... and then suffer a relentlessly high fatality rate, crippling technological inferiority, and severe funding troubles. AnyoneCanDie, often in rather brutal ways, and 50% or higher casualty rates are common in ''successful'' missions, with failures usually resulting in [[TotalPartyKill no survivors whatsoever]]. The cool-looking armor is [[ArmorIsUseless good for little else besides appearance]]. The CoolShip costs ludicrous amount of money to lease and is completely unarmed. The goofy-looking aliens outnumber us over a thousand to one and have technology that outstrips ours to such a degree that X-COM might as well be fighting them with ''sticks''. The Man in Washington will happily cut funding at the drop of a hat, even if there's a UFO landing outside the White House. [[DarkerAndEdgier It is not a very pleasant situation.]] Ironically, after Hasbro acquired the franchise they briefly attempted to make it into a children's cartoon series, which is a rather curious decision considering ''X-COM'''s almost insanely [[RuleOfThree high casualty rate]].
* DestroyableItems: Repeat after me: No grenades or rockets in the alien engine room. Explosions can destroy any object lying on the ground, including corpses, unconscious units, and loot. Oddly enough, ammunition and other explosives are unaffected by explosions.
* DisadvantageousDisintegration: Someone got hit with the Blaster Bomb to the face in the room full of stuff MadeOfExplodium? No trace of a body and equipment.
* DisasterDominoes: When enough units are low on morale, mistakes will start piling up and feeding on each other, until recovering from a losing battle becomes almost impossible.
* DiscOneNuke:
** Laser weapons and personal armor, in that order.
** Through a NewGamePlus or by starting a multiplayer server, the most powerful of upgrades are unlockable at the beginning on ''Enforcer'', including the nuker.
* DoingResearch: Any facility or weapon beyond the pitiful starting gear must be researched, which usually requires some alien material or corpse to reverse-engineer.
* DoomsdayDevice:
** TFTD: The sunken city of T'Leth.
** ''Intercptor'': The Aliens' Project Doomsday and our own Nova Bombs.
** ''XCOM 2'': The Avatar program, which the X-COM commander (that's you) [[GrandThftPrototype hijacks]] for their own purposes.
* DropShip: Skyranger and Triton from ''UFO'' and ''TFTD'' respectively.
* DudeWheresMyRespect: You're up against the [[RecycledInSpace outer space equivalent of]] the LegionsOfHell, including little gray men that indulge in abduction and cattle mutilation and killer crabs that give a FaceFullOfAlienWingWong. The Funding Nations don't really care about your situation, and sometimes consider siding with Aliens as a better alternative.
* DummiedOut:
** One of the many things left unused is the "Alien Reproduction" item and research line in ''UFO Defense'' -- strange considering the resultant [[HalfHumanHybrid Half-Human Hybrids]] wind up playing a key part in ''Apocalypse''. The sequels also include other things that were ultimately left out due to time and budget constraints.
** ''Apocalypse'' also contains Procreation Parks, buildings in Megaprimus where couples go to have their children grown in artificial wombs, matching the dummied out research text of the above: "The process could be easily adapted for human reproduction".
* DungeonBypass:
** Tired of slogging through Cyberdisks and Sectoids while being panicked and mind-controlled? Breach the hull at the top floor and reach their Leader immediately with a Blaster Bomb! Other weapons can also breach the less-durable inner walls of [=UFOs=], and human buildings are all too easy to destroy. A common early-game tactic is to spam rockets and autocannon grenades on buildings that aliens might be hiding in rather than engage in costly room-to-room or building-to-building combat.
** In ''Apocalypse'', collateral destruction is a viable strategy, if you didn't mind getting stuck with the bill. Instead of scattering troops across large, multilevel facilities to hunt down aliens in dark corners, you could set fire to or blow the floors out from under their suspected hiding places and wait for the sound of their screams. [[ThereIsNoKillLikeOverkill Or just level the building with combat vehicles]].
* DynamicDifficulty:
** Regardless of the difficulty a given campaign starts at, most of the games will see fit to ramp up alien activity to correspond with consistent positive performance.
** If the player puts off going for the BigBad in ''Terror From the Deep'', alien bases will start to proliferate faster than the player can keep up with them. In other words, X-COM are fighting a losing war against superior technology. If they do not exploit their weak point by finding the BigBad, the enemy will become stronger and stronger until players have no chance of survival.
* EarlyGameHell: The ''X-Com'' franchise is known for being rough on beginners.
** In ''UFO Defense'', the kid gloves come off about 4-5 months in, and you're expected to have your house in order. Aliens will begin dragging along Heavy Plasmas as early as month two; meanwhile, your researchers have cracked laser weapons at ''best''. Pistols and machine guns are functionally useless by this period.
** Your starter base is comprised of three hangars, one at each corner, with a lift in the middle. It's very elegant. In practice: the worst imaginable schematic. Good luck fending off an invasion fleet with four separate modes of entry. Expect to sink five hundred grand into demolishing and moving those helipads. It should be mentioned that ''[=OpenXCOM=]'' offers an option to design the first base from scratch. It annoyed a lot of people.
* EarthShatteringKaboom: ''Interceptor'''s Nova Bomb is designed to take out a star and everything orbiting it (a lower-level Class X-2 on the ApocalypseHow scale).
* EasyLogistics: Averted. While ammunition for conventional weapons can be bought as long as there is money, more advanced weapons require manufactured or captured ammunition to work. And then there's allocating a limited stockpile of Elerium between manufacturing and aircraft fuel.
* ElaborateUndergroundBase:
** A necessity due to X-COM's covert nature, often leading to AllYourBaseAreBelongToUs should the aliens stumble upon it (hopefully there is more than one base built by the time an Alien Retaliation fleet comes calling).
** Aliens have underground installations which need to be broken into to kidnap high-ranking officers for interrogation to complete the game.
%%** ''Enforcer'' does this in a few levels.
* EliteMooks:
** Alien Squad Leaders in general.
** Enforcer bosses, which are usually giant versions of other mooks like Reapers or Chryssalids, with special attacks.
* EmotionBomb: "Panic Unit", the easier use of psi powers.
* EnemyDetectingRadar: Motion Trackers, though they can only detect units that moved within the last turn. So always check the corners in case something's lurking.
* EnemyScan: Mind probes, which allow the player to view an enemy's stats.
* TheEnemyWeaponsAreBetter: Damage-wise at least.
* EnergyWeapon: Laser and Plasma weapons.
* EncyclopediaExposita: The [=UFOpaedia=] in its various forms across the generations. Even more so [[http://www.ufopaedia.org the fansite of the same name]]. And [[http://ufopedia.csignal.org/ there is more or less an online version]] of the in-game [=UFOpadias=].
* EnsignNewbie: Your newly hired and unranked recruits, thanks to their randomly created stats, are potentially capable of being incredible marksmen, MadeOfIron or -- when you have researched a Psionic Laboratory -- mindraping any alien they see into committing treasonous and suicidal acts of violence against their own side. (But more likely they're completely useless and you'll have to sack 8 out of 10 when you finally get their psi evaluations.) If you know what the limits are for a fresh recruits stats (for example, they can start with 40 to 70 time units), then you'll quickly realize that most of your recruits literally ''are'' cannon fodder, being at the bottom rung of effectiveness.
* ExclusiveEnemyEquipment: The few things that your technicians cannot reproduce, including the alien fuel material. Everything else, up to and including their power sources, navigation and weapons are reverse engineered, adapted and fielded within a few days or, in the case of your own flying craft, a few weeks. Subverting this is X-COMs specialty.
* ExplodingBarrels:
** Fuel drums in your bases, gas pumps in Terror Missions, and certain UFO components all explode when shot. Frustratingly, so do Elerium pods exposed to explosions.
** In ''TFTD'', the normal skirmishes (USO Recovery) sometimes have what seems to be oil pumps. Also, apparently sunken aircraft's engines are MadeOfExplodium.
* ExposedExtraterrestrials: Sec[=/=]Aquatoids, the rest of non-terrorist ''TFTD'' aliens and all of ''Apocalypse'' ones.
* FaceFullOfAlienWingWong:
** Chryssalids don't necessarily use the face, but they do reproduce by forcibly implanting eggs in human hosts that burst upon death to reveal a new-born Chryssalid ready to fight..
** Tentaculats and Brainsuckers reproduce in similar fashion in ''Terror from the Deep'' and ''Apocalypse'', respectively.
** Brainsuckers attach onto people's heads and empty their innards down their throats.
* FakeDifficulty: ''Terror From the Deep'' is probably the worst offender, but the game balance would not suffer if the standard rifle from ''UFO Defence'' were capable of reliably hitting anything a distance greater than it could be thrown.
* FanRemake / FanSequel: Free ones include and are not limited to ''[[http://ufo2000.sourceforge.net/ UFO2000]]'', ''[[http://ufoai.sourceforge.net/ UFO: Alien Invasion]]'', ''[[http://openxcom.ninex.info/ OpenXcom]]'', and ''[[http://ufotts.ninex.info/ UFO: The Two Sides]]''. Commercial ones include and are not limited to the ''VideoGame/UFOAfterblank'' series, the ''[[http://ufo.ufo-extraterrestrials.com/ UFO: Extraterrestrials]]'' [[http://www.ufo2extraterrestrials.com/ series]], and ''VideoGame/{{Xenonauts}}''.
* TheFinalFrontier / SettlingTheFrontier:
** ''Apocalypse'' is based on an alien planet in the process of being colonized by earth corporations.
** ''Interceptor'': One of our side jobs is to protect the developing outposts that will later mine Elerium.
* FiveRoundsRapid: Go ahead, try using ballistic ammo on a Muton.
* FlamingSkulls: Skull-shaped explosions.
* FriendlyFireProof: Averted, and with the average accuracy of X-COM soldiers, frequently painful.
* FrickinLaserBeams: The Laser weapons obviously. In the first ''X-COM'', they're extremely useful throughout the early and mid-game and retain effectiveness in the late game, as they use no ammunition. Laser pistols also have the added advantage of an very low TU cost to their autofire, making them ideal for room-to-room combat against anything short of Mutons and Snakemen missions with Chryssalids. Sectopods, the Ethereal's terror units, are more vulnerable to laser beams than plasma.
* GameplayAndStorySegregation[=/=]{{Retcon}}: The manual for ''Interceptor'' states that the First (''UFO'') and Second (''TFTD'') Alien Wars lasted 3 and 6 years, respectively. In-game, you'll likely reach the limit of your research and win or lose within the first year, early second if things drag out.
* GatlingGood: The Autocannons and their successors. Regular and incendiary ammo rapidly become obsolete, but high explosive rounds remain viable throughout the game. Being able to saturate an area with high-explosive bullets never ceases being effective or awesome.
* GenreShift: What happened to every single ''X-COM'' game after the third one.
* GeoEffects: On the Strategic scale, where you land determines what kind of terrain it will be in the battlefield. For example in ''TFTD'' landing in seas around Europe makes it very likely that the mission will take place among the UnderwaterRuins, and in the very deep areas it's dark as in the night mission even during the day.
* GiantMook:
** Many terrorist aliens.
** The Megaspawn from ''Apocalypse''.
** ''Enforcer'' bosses.
** ''UFO Defense'' gives us the Reapers and Sectopods, the former a glorified alien attack dog and the latter a heavy assault mecha. Terror from the Deep has the Xarquid, a giant nautilus, the Triscene, a [[EverythingsBetterWithDinosaurs dinosaur with Sonic Cannons]], and the Hallucinoid, a prehistoric jellyfish with [[AnIcePerson chemical freezing agents]].
* GiantEnemyCrab:
** The Chryssalids in ''UFO Defense''.
** The Lobstermen in ''Terror from the Deep''.
* GlobalCurrency: Everything bought and sold in the main games is apparently done so in [[WeAllLiveInAmerica U.S. dollars.]]
* TheGoomba: Sectoids in most continuities. In the Geoscape, the "Very Small Scout" is the UFO equivalent. In fact, the score for capturing it intact is lower than what you would get for blowing the sucker to pieces.
* GrenadeHotPotato: With a little coordination and luck, a soldier in the back can prime and pass a grenade to the front.
* TheGreys: The sectoids are the classic little grey aliens with the big heads. They're the weakest enemies in the game and have psionic powers.
* GridInventory: Multiple grids throughout the body and uniform (and multiple Time Unit costs for movement of items from location to location) make a refreshing take on the InventoryManagementPuzzle. The ''true'' InventoryManagementPuzzle (at least in the first game or two) was deciding what 80 pieces of gear to bring along on a mission. A fully loaded Avenger/Leviathan (holding 26 soldiers) could consume 52 of those slots just giving each soldier a gun and its ammunition. And that's without bringing extra ammo for reloading.
* GunsAkimbo: Doing this in ''UFO'' and ''TFTD'' only gave you another weapon to fire from with penalties. Expended in ''Apocalypse''.
* HarderThanHard:
** Superhuman. "Ironman" Mode saves the game after each turn, thus preventing the player from fixing mistakes.
** ''Enforcer'': [=XtraSpicy=] is unlocked after beating the game on hard. The most obvious difference is NumericalHard.
* HighTurnoverRate: If you're not good enough or just plain unlucky, most X-COM soldiers will not last more than a month or two, leading to this.
* HiveMind
** The aliens in ''UFO Defense'' take orders from one, another in ''Terror from the Deep'' tries to tell a CosmicHorrorStory while it's at it, and the Biomass in the ''UFO'' games is a weapon designed to [[GeniusLoci turn a planet into one]].
** The true threat in ''X-COM Apocalypse'' are actually colonies of microscopic organisms that are sentient in groups. Every alien life form you encounter in that game is merely one they've managed to take control of and manipulate to their own ends; the "brainsucker" life form that turns your comrades against you just injects their brains with an overload of micronoids. Late in the game, some [=UFOs=] try to take control of buildings and organizations by directly sprinkling lots of micronoids onto the building in question to influence the minds of those within.
* HoldTheLine:
** The objective of any Base Defense mission. Can literally turn into Hold The Line if you choose to adopt such tactics, although in some cases it's not so much line-holding as shooting fish in a barrel with a BFG. This probably only applies if your base is attacked early in the game where aliens' psi attacks turn it into a nightmare. But, once you screened your recruits (and sack the weak minded ones) and researched alien weapons, even if you have poorly designed base, a defense mission is just a shooting gallery.
** Two early missions of ''Enforcer''. The first requires to defend against incoming waves while travelling on a hoverboat, and the second in the following mission where you defend four humans in a forcefield. A late mission requires you do destroy on an aircraft while defending the pilots. (Only "hold the line" missions have vulnerable civilians. In all other cases, they'll [[InvulnerableCivilians simply scream]] due to nearby weapon fire.)
* HollywoodHealing: Averted, wounded soldiers have to stay on lengthy medical leaves, with the most serious cases taking months.
* {{Hovertank}}: With your choice of Fusion Bomb launcher or Plasma cannon. Arguably, the Cyberdisc can be considered one of these sans turret.
* HumanoidAliens: Most of the weapon-using aliens you face are humanoid in appearance, and in some cases were human before being genetically modified. The rest, with few exceptions, are non-humanoid terrorists units that support their masters.
* HumanResources: Many research reports state that the aliens "harvest" humans for various purposes, from research to organ extraction.
* IdiosyncraticDifficultyLevels:
** [[EasierThanEasy Beginner]], Experienced, Veteran, Genius, [[HarderThanHard Superhuman]].
** ''Apocalypse'' is a bit simpler: [[EasierThanEasy Novice]], Easy, Medium, Hard, [[HarderThanHard Superhuman]].
* ImmuneToBullets: Because of how armour works and damage is rolled, certain enemies are actually immune to standard rifle or pistol rounds. Some are even highly resistant to otherwise powerful alien weapons (hello, Sectopods and Lobstermen).
* ImportedAlienPhlebotinum: About 75-90% of gameplay revolves around the acquisition, understanding, and implementation of cool alien toys. Or in the RPG terms: Kill them, take their stuff, reverse-engineer it, Repeat. Reversed in ''Apocalypse'': when you sell some of your stuff to a MegaCorp that's been infiltrated by aliens, the aliens will import ''your'' phlebotinum.
* Instant180DegreeTurn: Averted. Turning costs Time Units, though it will not trigger alien reaction fire. Sometimes, troopers who have to turn to face the enemy wind up without sufficient [=TUs=] to take the shot.
* InstantSedation: The enemy is stunned if the stun damage exceeds the normal health. Thus, it is usually played straight for weaker aliens and those with weakness to stun damage, unless you are unlucky, but generally averted for stronger ones.
* IsometricProjection: The perspective used for Battlescape.
* ItemCrafting: Manufacturing the reverse-engineered alien technology and our own creations.
* ItsUpToYou:
** Since all of the world governments have tried and failed to handle the aliens, it's up to X-COM to get things done. Although it wouldn't hurt if the local governments lent a hand during Terror Missions.
** ''Terror from the Deep'': X-COM was disbanded after the end of First Alien War, and the world governments don't have the advanced technologies they developed to confront the new alien threat. Once again, it all comes down to X-COM.
* IWantThemAlive: When researching Alien Origins and latter item down the paths, the reports state that you need to capture higher ranked aliens.
* JetPack: Your troops get these during the late game (or from the start in case of ''Apocalypse''). The flight-capable aliens (except for the psychic aliens who use their powers to fly) usually have these... [[HollywoodCyborg built]] [[BodyHorror in]].
* TheJoysOfTorturingMooks: If you can survive long enough to craft blaster bombs and flying suits, breaching [=UFOs=] turns into a turkey shoot. Until then, you may content yourself with setting jungles on fire, torching UFO interiors to cook aliens from inside the shell, leveling their sniper's nests with TNT...
* KillItWithFire: Burning the zombies (with incendiary ammunition) will also kill the chryssalid\tentaculat without it popping out.
* KillStreak:
** The total number of "kills" in each soldier's profile.
** ''Enforcer'': The "hot streak" is increased by killing aliens, but is reduced by taking damage. As it increases, it treats weapons as being at least one level higher than the research level.
* LawEnforcementInc: After the Second Alien War of ''TFTD'', X-COM becomes this to avoid underfunding. X-COM's more ambitious cousin Marsec started out as a replacement for the former in guarding the martian colonies so that they could concentrate on potential alien threats, but soon becomes a para-military corporation with a ruthless reputation. Megapol from ''Apocalypse'', in addition to being a police force, also operates other 24-hour services, the fire fighters and the hospitals.
* LensmanArmsRace: As X-COM improves their arsenal and knowledge via research and reverse-engineering, the aliens will start sending bigger [=UFOs=] with larger groups of better-trained soldiers wielding bigger guns with nastier support monsters, after which X-COM will improve their arsenal and knowledge via researching and reverse-engineering of anything this new wave had on their dead bodies. Rinse and repeat.
* LetsSplitUpGang: A ''[[LemmingCops great]]'' tactic, in movies as well as computer games! Seriously, though, bunching up your squad isn't such a good idea, either, as they tend to attract grenades[[labelnote:*]]Except in the first game, where an AI bug means that aliens will ''never'' throw grenades. You're still vulnerable to Small Launchers and Blaster Launchers, though, so watch out[[/labelnote]]. A balance between the two is best.
* LightningBruiser: Mutons and especially the Lobstermen.
* MadeOfExplodium: Lots of objects on the battlescape will explode when shot. Special mention goes to the Cyberdisc and its successor, the Bio-Drone. When they die, they explode with stunning force, causing collateral damage. This can help for better or for worse, depending on who the explosion kills.
* MarathonLevel: The two-parter missions.
* MarketBasedTitle: The original game was called ''UFO: Enemy Unknown''.
* MechaMooks: Various Terrorist aliens, most of them being mini-FlyingSaucers.
* MeetTheNewBoss: Pretty much every knew alien threat faced in the original series, when it comes down to how they act and what they're goals, are essentially same product new packaging of the original aliens.
* MercyMode: Having a particularly bad month performance-wise or worse, a string of bad months, will make the game take pity on you by making the "X-COM agents discover the Alien Base". Technically possible even if you're doing fine, but much more common when you're doing bad.
* MindControl: The ''harder'', but much more useful, use of psi powers.
* MindProbe: A handy tool for either side to [[EnemyScan gather information on the other]]. Best used for determining how close an enemy is to collapsing from stunning, or whether that alien right there is a Soldier/Medic (Mook), Engineer (useful for research), or a Commander (Boss, crucial to capture in the late game). Becomes obsolete once you get high-psi strength units equipped with psi-amps, which can take total control of an enemy and allow you to see its stats at any time for the remainder of the turn.
* MonsterCompendium: Via [=UFOpaedia=].
* MoneyForNothing: UFO parts and corpses sell quite well and X-COM itself can self-finance through arms manufacturing.
* MoraleMechanic: Casualties and psychic attacks can cause your soldiers to panic, moving and shooting at random. The presence of a high-ranking officer can reduce morale loss from casualties, but an officer's death has a larger effect on morale.
* MultinationalTeam: You recruit from around the world. However, recruit names are exclusively drawn from Russian, French, German, Japanese, and British/American pools (the last two being a little difficult to distinguish). ''TFTD'' adds Spanish and Italian pools.
* MyBrainIsBig:
** The Sectoids and Aquatoids are small, impish humanoids with enormous heads. Certain variants have psychic powers.
** Ethereals aren't exactly under-endowed in the grey matter department. Their design in ''Interceptor'' has a brain large enough to apparently need air-cooling.
** The Alien Brain, which is precisely what it sounds like, and the final boss of ''UFO'', is very big indeed.
** The Psilords (''Interceptor'') are apparently all brain.
* MythologyGag:
** The "Gollup" chamber.
** Marsec's first appearance was in ''Laser Squad'', the spiritual predecessor to ''X-COM''.
** ''Enforcer'' features a mishmash of resources from two fellow ''X-COM'' titles scrapped during its development, ''Genesis'' and ''Alliance''.
* NGOSuperpower: X-COM in a nutshell. Able to freely cross borders, intervene militarily with impunity, and dedicated to ''Earth's'' defense, rather than any particular country, X-COM is answerable only to its budget. As long as the organization maintains a positive account balance and has at least one supporting country[[labelnote:*]]and in Apocalypse, you can even ignore ''that'' requirement[[/labelnote]], it will continue to fight against the alien invasion. Justified by the desperate straits of the situation, and the funding councils are quick to pull support if they can justify it [[spoiler: or the second the invasion seems to have been thwarted]].
* NoHeroDiscount:
** Your starter fleet. Until you begin building your own crafts, you're stuck ''leasing'' the hand-me-downs from Earth's military, built entirely from crap Terran technology.[[labelnote:*]]The Interceptor and Skyranger actually represent the pinnacle of available Earth technology in the XCOM universe, they're just hopelessly outmatched by alien weaponry[[/labelnote]] Each one costs a half million a month, and it adds up fast. They must be insured, though, because you can completely trash them with zero penalty.
** In general, this is played straight for any Terran gear you want to buy, and for the wages of your staff. You're expected to stay within your budget or else find alternative ways of funding your operations.
* NonLethalWarfare: Stun Rods (melee spears), Stun Bomb Launchers (basically a grenade launcher that fires stun bombs) and their successors. The only other way to capture aliens is to make them pass from pain from normal weaponry.
* NothingIsScarier: Night missions can be exceptionally creepy, especially in ''Terror from the Deep''. It's pitch dark and there are aliens packing enough firepower to drop soldiers in one hit, and furthermore, since it's so dark, you don't know where they could be hiding. It can get even worse if you're on a Terror Mission with Snakemen, and you know that there are Chryssalids just waiting for you to screw up.
* OmnidisciplinaryScientist: The same staff of scientists does everything from reverse-engineering captured weapons to designing new aircraft to interrogating prisoners. Although considering that you NEED a lot of them to have a decent research progress, it could be handwaved that, say, a research on Plasma Weapons is led by the specialists in the field with everyone else following instructions. In ''Apocalypse'' we got three types of scientists: Engineers, Quantum physics and Biologists.
* OneHitPointWonder: Your units actually have a life bar but, until they gain lots of experience or get some BETTER armor, they might as well have one hit point. This is only averted at the start of the game by the very rare occasion of a soldier surviving a Plasma/Sonic shot in their starting armor due to a low damage roll.
* OneHitKO:
** Chryssalid melee attack. The same goes for its successors.
** Soldiers can be easily killed in one hit from a Plasma gun, even if he is wearing a Power Suit, if the damage roll is high enough.
** Vibro Blades in ''Terror from the Deep'' are capable of killing most aliens in one or two hits, including the [[ImplacableMan Implacable Lobstermen]].
* OneStatToRuleThemAll: Psionic Strength in the first game (and its cousin MC Strength in the second) is the only stat that cannot be trained and it determines both resistance to alien mind control and the soldier's ability to control aliens. Actively using psionic abilities provides experience for all but three other stats.
* OneSteveLimit: Averted due to limited names pool. With only a relatively small amount of names to pick from when a new soldier is randomized, it's not uncommon to see several share a name.
* OnlyAFleshWound: Averted. Arm and leg wounds will greatly reduce a soldier's fighting ability, just like head and torso wounds. And that's on top of bleeding to death.
* OrganicTechnology: All sorts of purpose-bred aliens in the first two games, and practically every aspect of the alien threat in ''Apocalypse''.
* OrganizationWithUnlimitedFunding: ZigZagged; the Funding Nations[=/=]Senate are huge cheapskates, but once enough engineering facilities get going and start cranking out weapons to sell, X-COM can effectively go rogue. However, the better the player does at protecting a given nation, the more they'll increase funding. As the game only ends when the player is in the red for too long or if all nations sign non-aggression pacts with the aliens, it's possible to keep protecting a few nations at a time and building up their funding over time to replace the nations that drop out. In a sufficiently long game, it's not uncommon to have the US providing 14-20 million dollars a month to X-COM... as the only nation still funding it.
* PacifistRun:
** ''UFO'' and ''Terror From the Deep'': To progress, the player needs to capture enemy aliens alive to interrogate or inspect them. Cue the player loading up on stun rods and other nonlethal equipment (depending on which installment in the franchise) so they can capture most or all aliens alive in one mission (and then get back to the slaughter once research is complete).
** In ''Apocalypse'' if a player raids an organization without killing anybody or damaging any property, the relations aren't penalized, despite the stolen loot. Plus ''Apocalypse'' has stun grenades, ranged stunners and mind control available from the start. Many players raid Marsec for all the cool weapons not available from the start or in short supply. There are also [[PsychicBlockDefense Mind Shields]], which were DummiedOut and cannot be bought.
* PeopleJars: You will find these in the Alien bases. Unfortunately, they contain what left of their occupants.
* PlayerHeadquarters: Though there is no HQ in the strict sense once you have multiple bases, the cost and time associated with building bases and the subsequent maintenance fees will make the first starter (and already developed) base your main base of operations. Which is ''bad'', because it's the most likely base to be attacked, and has an ''extremely'' difficult-to-defend layout.
* PlayerMooks: Soldiers, available in unlimited quantity and variable quality until trained in battle.
* PoweredArmor: Later armor suits in ''UFO Defense'' (and the whole lot of 'em in ''Apocalypse'') use Elerium-115 to power shielding, muscle enhancers, and the occasional flight module. Flight and protection are the only benefits; armour has no bearing on a soldier's strength or other stats (the muscle enhancers are just [[InformedAbility fluff that indicates a lack of weight-related decrease in soldier performance]]).
* PowerCrutch: The [=PsiAmps=] and their variations that enable X-COM soldiers to use psychic powers.
* PowerUp: All powerups, whether weapon or conventional, need to be researched in order to be equipped and/or randomly dropped (in ''Enforcer'').
* ProperlyParanoid: Anyone who takes ''great'' care while handling Terror Missions. If you aren't covering all the angles, you're just TemptingFate.
* PsychicAssistedSuicide: Aliens won't shoot themselves, but they can be made to drop primed grenades at their own feet or drop their guns (only in the first game).
* PsychicPowers:
** Of the telepathic kind, making victims panic (or go berserk) to controlling them.
** The second game [[CallAHitPointASmeerp renamed Psi]] to Molecular Control, which [[AndIMustScream is suitably more horror-inducing]].
* PsychicBlockDefense:
** Androids in ''Apocalypse'' cannot be controlled at all, on account of being robots.
** The protagonist of ''Enforcer'' is [[implied]] immune to mind control, considering the situations the player gets into.
** [=HWPs=] and [=SWSs=] in ''UFO'' and ''Terror From the Deep''. Being unmanned vehicles, mind-affecting powers do not affect them.
** One of the novelizations has a guy who happens to have a Psi Strength of zero. [[CursedWithAwesome It makes him unable to use psi powers at all but they don't work on him either.]]
** There are only two aliens in ''Apocalypse'' that are easily affected by Psionics, them being the Anthropod and Skeletoid. All other creatures are resistant to Psionic attacks because they are either less intelligent (which somehow boosts resistance), in the case of Multiworms or Spitters, or possess Psionic abilities themselves, like the Micronoid Aggregate and Psimorph.
** ''Apocalypse'' has Mind Shield -- an item increasing psionic defense when used in the battlescape. Due to a bug the increase is permanent and cumulative, thus any operative can become invulnerable. The item was supposed to be removed completely from the game, but due to another oversight may be encountered during missions in Marsec buildings. Fans have come with an in-universe explanation that permanency and cumulation were unexpected side effects, Marsec found them disastrous for their business -- killing the market both for Mind Shields and Mind Benders -- and recalled all unsold items shortly before the game start.
* PurelyAestheticGender: Recruits can be either male or female. This has absolutely no effect on starting stats or stat growth. All it does is paste a slightly different head on the sprite and give ladies a different scream when they die. (In the second game, at least. In the first game, all aliens and all soldiers sound the same when they die.)
* RandomizedDamageAttack: The weapon stats displayed in game show average damage. Guns roll from 0 to 200% of that, while explosives roll 50-150%. Lucky, unarmored soldiers can survive point-blank heavy weapons fire while unlucky, armored ones die to stray pistol rounds. ''TFTD'' adjusted it so all weapons roll 50-150%, making the above mentioned situations less common, but not impossible.
* RandomlyGeneratedLevels: Using an algorithm to procedurally construct levels from "tiles". Just as likely to spawn your exit ramp in front of a Muton priming his grenade, alas.
* RandomNumberGod: In addition to accuracy rolls, all weapons and explosives do a random amount of damage. A lucky soldier can survive multiple bursts from heavy weapons, whereas an unlucky one dies from an ally's missed shot. For a comprehensive, heartburn-inducing list, there is even a [[http://ufopaedia.org/index.php?title=Murphy%27s_Laws_%28X-COM%29 Murphy's Laws]] of ''X-COM''.
* {{Realpolitik}}: There is a little bit of this in how the [[http://www.ufopaedia.org/index.php?title=Country_Funding_(EU)#Monthly_Funding_Change Council of Funding Nations reevaluates its funding of X-COM]]. Ex: X-COM performed excellently in March except for that time where the few particularly large [=UFOs=] flied over Country A unopposed causing trouble, giving Country A enough reason to reduce funding, but since the Council's majority opinion of X-COM is overwhelmingly positive that month, Country A has no choice but to stay quiet, not increasing the funding as their only means of protest. The only exceptions are when X-COM performs extremely badly at the complaining Country or if Alien infiltrated it. The reverse is also true, where very few will dare to increase funding when the Council is very unsatisfied with X-COM.
* RealTimeStrategy: The Geoscape[=/=]Cityscape screen is real-time, pausing for events like delivery of ordered items, an alien sighting, or the arrival of troops at a mission site.
* RedEyesTakeWarning:
** The Reapers in ''UFO''.
** The Aquatoids in ''Terror from the Deep''.
* RedShirtArmy: At the start of the game, the player's soldiers are all ridiculously fragile, and as likely to die as to inflict any damage at all. If you arm them correctly, they ''may'' survive a shot or two. Assuming you aren't save scumming, an efficient play-through will likely burn through dozens--if not a hundred--rookies and vets by the end. This is normal, and as the weary saying goes: you don't fly to Cydonia, you climb there on a mountain of dead rookies.
* RegeneratingHealth: Available in ''Enforcer'' as a researchable passive ability.
* RidiculouslyFastConstruction: Building a base gives you an instant lift. Other than that, the game avert this.
* {{Roboteching}}: Blaster Launchers and their equivalents with their diabolical waypoint-based targeting system.
* RPGElements: Soldier stats in all games.
* SaveScumming: A common strategy, unless you think this is cheating or dishonorable -- it is possible to win the game with 0 casualties. The game designers do make a token effort to discourage it; you can't load a saved game during a combat mission, although you can ''save'' all you want in the middle of a mission.
* ScaryDogmaticAliens: The bad endings classifies the aliens as the Conqueror type, who attack Earth for its resources.
* SecretWar: All of them start as one, but according to the manuals all of them become open secrets later.
* SensorSuspense: Motion detectors: a good way to avoid becoming Cannon Fodder when facing alien weapons, but since you don't know whether the blip is from alien or civilian and on which floor, dealing with the results can be... interesting. Two words: Hidden Movement.
* SeeingThroughAnothersEyes: Through mind-control.
* SelfImposedChallenge:
** Probably the greatest fan-mod undertaking for ''UFO Defense'' is fixing a bug that locked the starting difficulty of the game at "Beginner".
** There are a bunch of challenges listed with one of the well-known editing utilities, including things like refusing to research any new tech (thus making the game technically unwinnable, but few get to such a point since it's damn difficult without) and not killing any aliens (winning is still possible since they can be stunned).
** Zero loss run: No X-COM agents lost, no civillians lost. Hope you have a few months spare.
** [[http://ufopaedia.org/index.php?title=User_talk:Arrow_Quivershaft#1_Mission_X-COM One Mission X-COM]]: It's possible to complete the game after completing only one mission: a well-executed UFO Ground Assault on a battleship can yield all the alien prisoners and raw materials needed to research Cydonia and complete the game. The difficulty is in pleasing the Funding Nations (no terror missions or alien base assaults allowed), and in keeping away from bankruptancy.
* [[CapcomSequelStagnation Sequel Stagnation]]: Averted. After ''Terror from the Deep'', which was basically [[MissionPackSequel an underwater rehash of the first episode]], new elements and even {{Genre Shift}}s were introduced -- unfortunately, they didn't result in good games.
* ShinyLookingSpaceships: [=UFOs=] of the first game. X-COM fighters in ''Interceptor''.
* ShoutOut:
** [[Fracnhise/StarTrek The warp nacelles on the Avenger craft and the cylindrical Elerium reactors.]]
** On the Firestorm, the primitive substitute for a UFO engine sits dead-center in the craft and bobs up and down, much like a [[Series/DoctorWho TARDIS]] console.
* SmokeShield: Caused by specialized smoke grenades and explosive terrain features.
* SortingAlgorithmOfEvil:
** In ''UFO Defense'' it's Sectoids and Floaters and early Snakemen if you're unlucky > Snakemen if you're lucky > Mutons > Ethereal.
** In ''TFTD'' it's Aquatoids and Gillmen > Tasoth and Lobstermen.
** Also lampshaded in Guava Moment's ''Apocalypse'' LP.
* SpiritualSuccessor: Many. The ''UFO: Afterblank'' trilogy to name one.
* SplashDamageAbuse: The great vulnerability of ground-based vehicles in ''Apocalypse'', including the tank. Also, most units take more damage from explosives that go off at their feet because of lower under armour.
* SprintMeter: While Energy[=/=]Stamina is used for everything, its biggest consumer is moving around. It only partially regenerates at the start of each turn (Less when carrying heavy gear), so if an X-COM soldier moves a lot without stopping (such as when reserving Time Units for an Reaction Shot), they eventually will be too tired to move more than a few tiles.
* StarKilling: The Nova bombs in ''Interceptor''.
* StrongFleshWeakSteel:
** With experience and armour, soldiers eventually gain much better stats than tanks and become more durable. However, tanks do retain a few advantages in that they cannot be stunned, mind controlled, or bleed out.
** Inverted in ''Enforcer'', where you will chew through Sectoids, Snakemen, and Chryssalids with one shot each while their feeble attempts to harm you bounce off your armored hull. [[LetsPlay It will give your]] [[ShoutOut positronic brain much amusement.]]
* StatGrinding: How the soldiers improve their stats.
* StockSoundEffects: Some of the sounds that occur while navigating the menus of the original ''X-COM'' have spread far and wide across various media, recently being used in the title character's HUD in the big-budget movie ''Film/IronMan''!
* StrayShotsStrikeNothing: Averted. With the exception of map borders where the shots disappear, all missed projectiles will continue to fly until they hit something: walls, explosive materials, civilians, X-COM operatives, aliens, etc.
* StunGuns: From Stun Rods to Stun Bombs, a variety of nonlethal arms gradually come into X-COM's possession and employ for the capture of necessary live aliens.
* SubsystemDamage: Head, Body, Separate Arms and Legs, with penalties one soldier's efficiency depending on injuries. Assuming the soldier in question survived the first shot.
* SuperSoldier:
** Mutons and Lobstermen. Your soldiers will become this if they are lucky enough.
** ''Enforcer'''s protagonist, who racks up over a hundred dead aliens a mission, and sometimes as many as four hundred fifty.
* TacticalWithdrawal: When the situation gets hopeless on the battlefield there is a option of retreating. The good side of this is that your soldiers live to see another day, the sponsors will be less angry than with total defeat and thus complete loss of expensive equipment, and that you could yoink some alien artifacts. Just be aware that everything that was outside the X-COM transport will be lost and MIA.
* TakeCover: Very important, given the computer's cheating tendencies and the power of alien weapons. Unfortunately, most forms of cover can be destroyed.
* TankGoodness:
** [=HWPs=] are a refreshing alternative to the hopeless rookies in the early game, at least in ''Enemy Unknown''.
** ''Terror From the Deep'': [=SWSes=] do make good scouts if you don't like sacrificing rookies for that. Once you get a Sonic Displacer, you will like it for its ability to float, get 200 shots clip which gets reloaded for free every missions, and ultimately, [=SWSes=] can't be harmed by tentaculats. If you already have the bigger ships, you will always want to bring one (or two) on every missions.
* TeamTitle: Subtitles aside, the series is named for the anti-alien unit commanded by the player.
* TechnologyLevels: Human Starter Tech < Advanced Human Tech < Alien Tech = Alien-based Human Tech.
* TechTree: While almost all physical alien artifacts can be researched as soon as you recover them, several conceptual lines of research require either the interrogation of live aliens or a series of prerequisites.
* TelepathicSpacemen: Ethereals, experienced Sectoids, their underwater cousins Aquatoids, Gill Men commanders, Tasoths, Psilords in ''Interceptor'', the list goes on...
* TerrorHero: Your psionic soldiers can use their psi abilities on the aliens to cause them to panic, making them easier to kill or capture. They can do the same to you, distressingly. Morale is another factor as aliens are as susceptible to losing their command structure as anyone else. Taking out a boatload of aliens without a single human loss can result in the alien leader going off his nut and panicking; killing the leader ''first'' (via floating up to the bridge and blaster-bombing the living hell out of it) causes his directionless troops to scatter.
* TickingClock:
** Even if your service is exemplary each month, you can't stop the funding nations from dropping out of the project. (Taking out the "Infiltrator" [=UFOs=] slows down the process, but it ultimately cannot be halted.) Lose enough donors, and you might go bankrupt. Lose ''all'' of them, [[NonStandardGameOver and the program is shut down.]]
** Averted in ''Apocalypse'', if only because it doesn't matter if everyone hates you as long as you have funding.
* TimeKeepsOnSlipping: The various incarnations of the Geoscape allow you to pass the time by anywhere from 1 second per second (slowest setting in ''Apocalypse'') to 1 day per second (fastest setting in ''UFO Defense'' and ''Terror from the Deep'') while you're waiting for the next alien sighting.
* TotalPartyKill: Get ready to get used to these because it'll happen a lot throughout your playthrough.
* TrickBomb: Smoke and Proximity Grenades. The former are for obscuring vision, the latter are throwable mines.
* TurnBasedTactics: The Squad-Level type during the battlescape.
* {{Unobtainium}}
** Elerium-115, the alien element that becomes a cornerstone for advanced technology and can only be looted from downed [=UFOs=].
** [[ElementsDoNotWorkThatWay Ununpentium has long been theorized to work that way, but currently doesn't.]]
** Also, ''Terror from the Deep'''s Zrbite.
* UnusableEnemyEquipment: Which will become usable after research.
* UnfriendlyFire and/or TheUriahGambit: Note that the [[AfterActionReport post-mission analysis]] does not have a spot for "X-COM Operatives Killed by X-COM Operatives." Your use of this oversight to justify friendly fire or the immediate court-martial of an alien-controlled operative will practically be a given.
* UrbanWarfare: Terror missions. Most of ''Apocalypse''.
* VideogameCaringPotential: Just ''try'' not to get attatched to your soldiers who got promoted to Sergeant or above rank.
* VideogameCrueltyPotential:
** What happens if you make a bunch of rookies designed ''explicitly'' to be cannon fodder and/or scouts (yes, the two jobs overlap frequently). This makes for some delicious BlackComedy as you can name the unfortunate saps such names like "Coward", "Ray Charles", "Dead Man Walking" and "Meat Shield".
** Parodied in ''WebAnimation/ZeroPunctuation''[='s=] ''Halo 5'' review, in which Master Chief is inexplicably ''dis''invited from the mission to find Cortana, and Yahtzee decides the UNSC must want to "level up some of their rookes". Cut to a queue of mini-Chiefs labeled "Fadge", "Jools", "Nobby", all of them Lvl. Ones. (Master Chief is labeled "[[foldercontrol]]

[[folder: Lvl. Like a Billion ]]
.")
* VendorTrash: All those alien corpses, spare UFO/USO compoments, and ammunition? Yeah, a good deal of that gets sold off to finance the organization. Even a relatively small UFO captured intact can net nearly a million dollars depending on how much loot you hold on to. Alien corpses are often extremely convenient for research, but supply exceeds all possible demand, so selling them is a non-trivial but disturbing source of income. (A strategy guide suggests that they make for excellent sushi. And a certain fan wiki suggests that bases frequently fighting Lobstermen requisition above-average amounts of butter.) Well, they do the same to us in the first place. They deserve every bit of what the scientists and chefs do to them.
* TheVeryDefinitelyFinalDungeon: The various Aliens' [=HQs=]. Failing the missions results in instant gameover.
* VeteranUnit: The Lucky Soldiers who survived enough battles and killed enough aliens.
* TheVeryDefinitelyFinalDungeon:
** Cydonia, the "Face on Mars".
** The city of T'leth.
** The Temple ship in the ''X-Com'' remake.
** ''Interceptor'': The Star system housing the Doomsday project, hidden [[spoiler: on the other end of the event horizon of a ''black hole'', not only necessitating your fighter piggybacking on another carrier to get in and out, but justifying the use of the Nova Bomb.]]
* VichyEarth:
** Gillmen are the worst. Not only are they lousy soldiers, but they're traitors to boot. Gillmen serve no advantage from a tactical standpoint, and are only working with the aliens to reclaim the surface world, which they deserted during an extinction event sometime after the [[{{UsefulNotes/Dinosaurs}} Mesozoic]] era.
** Earth slowly becomes this over the course of the games if you do badly or take too long, as more and more countries submit to the aliens. Apart from GloriousMotherRussia. Fan studies of long-term games have concluded that out of the Council of Funding Nations, Russia will ''never'' be infiltrated by aliens. The newspapers will instead probably show Sectoid ambassadors' corpses nailed to the gates of Kremlin.
* TheWarOfEarthlyAggression: Mentioned in the backstories of ''Interceptor'' and ''Apocalypse''.
* WeakWilled: Some soldiers and aliens are way easier to mind-control than others. On the plus side, the aliens tend to almost exclusively target the mentally weakest soldier on the team, who can be used as an unarmed mind control magnet while the rest of team is relatively safe.
* WeComeInPeaceShootToKill: During peace talks with the funding nations, one or more alien battleships will appear in the stratosphere and land. Battleships also sometimes engage in infiltration missions. Unlike the smaller [=UFOs=], they make a beeline for the nearest major city and land on top of it ''a la'' the Visitors from ''[[{{Series/V1983}} V]]''. An infiltrator battleship has a [[GunboatDiplomacy 100% success rate]] when forging pacts.
* WeHaveReserves
** Rookies make good scouts.
** The game mechanics actually encourages a WeHaveReserves mentality. If you feed ''TFTD'' rookies to keep it happy, the game can be quite manageable... but if you've truly mastered your tactics and so almost never lose a man, you're ''screwed''.
** This mentality is sort of averted in ''Apocalypse''. If you're good enough to consistently keep your squads alive in the early game, the difficulty ''will'' scale up quickly, but the aliens will be getting better weapons before better units (and an Anthropod holding a Devastator Cannon is still just an Anthropod), so if you really are that good, you can stay on top of the game all the time.
** The death of a rookie is less damaging to a squad's morale than the death of a higher ranking agent. And if you're [[VideogameCrueltyPotential feeling particularly cold]], the aversion of EasyLogistics makes it a lot easier, and cheaper, to send rookies in to combat with a bare minimum of equipment so that higher ranking and more skilled agents can get the good stuff.
* WeSellEverything: Played straight for most of the series. It makes one wonder what the people do with the alien artifacts you sell, especially the ''corpses''.
* WithThisHerring
** With this bunch of folks who would have failed the physical for any self-respecting military and have the reflexes of a dead fish, you must save the world...
** The standard-issue X-COM rifle is supposedly based on the best traits of a variety of human firearms, combined into one package perfect for your work. Unfortunately, it was built by the lowest possible bidder.
** Played even straighter in ''Terror from the Deep.'' The standard equipment you get is ''worse'' than their UFO counterparts, and about half of them only work underwater. In this game, it reaches Wallbanger levels: At first you're limited to your subs, darts guns and some harpoon launchers, since nothing you had before would work underwater. Then, you can have to fight the aliens on dry land, due a crash, a landing or a terror mission. Why, oh why you must still carry dart guns, instead of old Earth-made laser weapons, and wear a heavy submariner suit when you could have crates and crates full or armor from the first alien war? Heck, local millitias should be better armed and prepared than you at this point!
** Despite that fact that "Starlight" night vision scopes and binoculars have been available since at least the Vietnam War and passive infrared night vision has been around since the 1980s... you're reduced to throwing flares.
** In ''Apocalypse'' your starting weapons are a bit better, and Earth has some weapons on a par with alien ones. Money are short, but you can raid Cult of Sirius. But you can only buy what is available in the city stores, which get new shipments only on Mondays. You cannot buy best weapons and equipment (flying armor, mini-launcher, plasma pistol, plasma sword, powerful vehicle computer and engines, heaviest vehicles) until the start of the second or third week. And if you try to ZergRush [=UFOs=] with rocket and plasma hoverbikes, Megapol, Marsec and Solmine quickly run out of missiles and elerium to sell to you.
* WhoYouGonnaCall: Type 4, international government funded organization.
* YetAnotherStupidDeath: Players who are unlucky, forget to take precautions, or just play poorly, will get lots of these. Even a seasoned player will have some of these from time to time.
* YouAllLookFamiliar:
** Soldiers will have similar appearances on the inventory screen.
** Played Straight in missions. On the map they virtually all look alike. The guys all have [[Franchise/StreetFighter Guile haircuts]] and the women have ponytails. Ditto for civilians. (Veterans may remember the "Island of Identical Blue Bikinis" missions very well.)
* YouRequireMoreVespeneGas:
** Money, required to fund everything you do. Your official source is from the funding nations, who increase or decrease based on your performance. Your unofficial source is selling your spoils of war and manufactured goods on the black market.
** Alien Equipment, with the most important of them being the Elerium, the alien power source that cannot be reproduced, only salvaged.
** Hangars, Living Quarters and General Stores for increasing the Craft, Population and Item caps, respectfully. Similarly, having more Laboratories and Workshops will allows more Scientists and Technicians to be able to work.
* ZergRush
** On a larger scale, X-COM typically has extremely high casualty rates in all three games and [[ZergRush Zerg Rushing]] strategically to replace lost soldiers and interceptors is the only way to keep your head above water.
** One-robot Zerg Rush is probably the best way to play ''Enforcer'', as it lets you get those research points.
** You can take down the largest [=UFOs=] in ''Apocalypse'' using the smallest flyer available, hoverbikes. They're practically impossible to hit with the right settings. [[StarWars Worked for the Rebels.]]
[[/folder]]

[[folder:''UFO Defense'']]
* See ''[[VideoGame/XComUFODefense UFO Defense]]''
[[/folder]]

[[folder:''Terror From the Deep'']]
* See ''[[VideoGame/XComTerrorFromTheDeep Terror from the Deep]]''
[[/folder]]

[[folder:''Apocalypse'']]
* AbnormalAmmo
** Brainsuckers for the... Brainsucker Launcher.
** Also, the Entropy Launcher: A bioweapon firing homing missiles which release a compound that will dissolve through armor. It will also dissolve ''you'', should you be unarmored. As an added bonus, they'll make any explosives you're carrying... well, ''explode''.
* ActionBomb: The Poppers.
* TheAestheticsOfTechnology: The Aliens and their technology are organically ugly. The Mega-Primus city regulations mandates that everything should look retro-futuristic, which is most noticeable on flying cars.
* [[spoiler:AfterTheEnd: Thanks to the events of ''Terror from the Deep'', Earth is effectively a wasteland.]]
* AntiAir: Various weapon modules for the ground vehicles.
* AnotherDimension: The Alien Dimension.
* ApocalypseHow: Planetary, [[spoiler:finishing off the job from ''TFTD'']].
* ArmlessBiped: The Poppers. The larger weapon-platform type aliens don't really have proper arms either.
* AttackOfThe50FootWhatever: The Overspawn.
-->'''[[LetsPlay Director Zander]]:''' Oh please tell me that's not a fifty-foot monster.
** On a lesser scale, the Megaspawn and Psimorphs - the former being an organic weapon platform about 2-3 'floors' tall with built-in disruptor beam cannon and missile launcher. The latter is a powerful psionic entity a good 10-12 feet tall and packing SpareBodyParts.
* BeePeople: The Aliens.
* BlobMonster: Micronoid Aggregates. [[spoiler:They're really how the Brainsuckers take over their victims]].
* CorruptCorporateExecutive: Marsec, Solmine and Transtellar had a record of suppressing colonists rights.
* CorporateWarfare: The less scrupulous corporations wage secret wars against other corporations, and technically X-COM is itself a corporation in 2080s.
* CripplingOverspecialization: The Hybrids. They have great psychic powers and slightly greater reflexes than human soldiers, but are inferior in all other ways. Even worse, they improve their physical stats slowly, and you must assign them to a gym if you want to train their low strength -- i.e. they will either be unable to carry much, or they won't be able to train their psychic powers in the psy-gym. Finally, they need a special device to use their psychic powers, which means one of their hands will always be full -- i.e. they're usually restricted to using pistols, or suffering speed penalties.
* {{Cult}}: The Cult of Sirius, who believe that the Aliens are the saviors of humanity. They're the only faction in the game that will start off hating you. And, even if you spend (way) too much money to get their opinion to neutral, they'll never actually like you (the costs are prohibitive) and their opinion will nosedive as soon as you engage any alien forces. They're also (generally) hated by every other faction in Megaprimus. What this means...is that they are ''perfect'' raiding material for you to get additional money. Kill 'em all, let their god sort them out, and steal their stuff.
* DecapitatedArmy: Averted; you have to methodically and systematically destroy the entire alien infrastructure to win. Resistance wanes after the destruction of the Command Center, then resurges to reach its peak when you commence the final attack on the dimension gate generators themselves, with the surviving alien forces fighting like rabid, cornered animals.
* DeflectorShields: Disruptor Shields, for both individuals and vehicles.
* TheDevTeamThinksOfEverything: Selling a large amount of alien weaponry will result in it showing up in the hands of the various factions in the city, which can be either a very good thing or a very bad thing depending on your relationship with those factions.
* DoWellButNotPerfect: If you're very, very good, the Senate will decide that you're very cost-efficent and will reduce your weekly funding.
** Alien tech/type ramp-up is also dependent on scoring; do too well early on, and you're at risk of biting off more than you can chew.
* EnemyMine: Factions have a matrix of relationships, and an attack on given faction will cause those who are more hostile to the target to support the attack. If attacking aliens causes relationships to decrease with other corporations, then they like the aliens a bit more than they like X-COM.
* FantasticRacism: Sectoid Hybrids and Androids are at best treated as second-class citizens.
* FictionalPoliticalParty: Major parties of Mega-Primus Senate are NotSoDifferent rivals [[http://www.ufopaedia.org/index.php?title=Extropians Extropians]] and [[http://www.ufopaedia.org/index.php?title=Technocrats Technocrats]].
* FlyingCar: Relatively common vehicle type in ''Apocalypse''.
* FunWithAcronyms: The fact that a robots' rights group in ''Apocalypse'' would call itself the "Sentient Engine Liberation Front" clearly indicates that they deserve more credit than they're given.
* GunsAkimbo: The Real Time combat mode allowed this -- oddly, turn-based did not; carrying two guns penalized accuracy and only let you fire one at a time. Whilst troopers suffer (sometimes considerable) accuracy penalties for dual-wielding certain large weapons, it's quite feasible to use two autocannons at once if one so chooses. With a [[GameMod bit of tweaking]] for fully automatic fire and large magazines, you really have to be careful with that Explosive and Incendiary ammo.
* HeelFaceTurn: The Sectoids -- maybe. Played straight in the case of Sectoid Hybrids, who will serve you as loyally as any human soldier.
* HeroInsurance: Averted; you pay for the collateral damage.
* HotBlade: The Power Sword, a powerful blade weapon that is enhanced by a Elerium-powered plasma sheath.
* InfinityMinusOneSword: The androids are strong, tough, fast, very hard to tire out, almost impossible to make panic, and ''completely and utterly immune'' to two potentially devastating forms of attack; Brainsuckers, and Mind Control. Early and late-game, they make very dependable soldiers- but the price for this dependability is ''glacial'' stat-growth (so slow that most players will insist they have no stat growth at all) and inability to learn out of combat using combat facilities. Human soldiers will eventually come to outclass androids, but only after months of training and (potentially lethal) battlefield experience.
* InvisibilityCloak: The Personal Cloaking Field, which pops up very late in the game. It's not perfect (attacking from cloak causes it to shimmer and partially reveal the user) but it's pretty damn useful.
* IsometricProjection: In addition to traditional Isometric Battlescape, the Cityscape also uses this perspective.
* JustBeforeTheEnd: The aliens invade from a doomed, volcanic planet in another dimension where most other life has been scorched away by the local star's supernova.
* MegaCity: Mega-Primus itself, obviously.
* MegaCorp: About ten major ones in ''Apocalypse'', among a few others it'd probably be a good idea to defend against alien infiltration.
* MobWar: Rare, but happens sometimes.
* TheNudifier: The Entropy Gun. It's a homing bio missile which, on hitting, starts to dissolve all your armour and weapons.
* OrganicTechnology: Everything the Aliens use.
* OurWormholesAreDifferent: In the form of vaguely pyramid-like portals.
* PhlebotinumBomb: The Alien Gas grenades and missiles, hurt only aliens while doing nothing to humans.
* PointDefenseless: Laser Defense Arrays. The Plasma version is better.
* PuppeteerParasite: The Micronoids.
* RaygunGothic: The general art-style. There is something surreal about being attacked by a "Military-grade hovercar" which resembles a cherry-red 50s Plymouth convertible.
* RealTimeWithPause: One of two Battlescape modes. Each mode has its own pros and cons.
* ScrewTheRulesIHaveMoney: You can do this. No, ''really''. Even if ''every'' corporation in the city turns against you (either by subversion by the aliens or by hating you for any number of reasons) and the Senate ''ceases funding and threatens to shut you down'', you can keep fighting for survival so long as your bank account remains in the positive... and as long as you have a functional base and a steady source of income to sustain your private army, you can go ''renegade''. Want to show the Senate what you think of their threats? ''Go level half the city.'' [[EvilLaugh Mwhahahahahahaha!]]\\\
Sources of said income include: Raiding enemy corporations. Manufacturing and selling alien equipment. Selling captured alien equipment. Acting as a pusher for alien techno-drugs. It is strongly recommended that you cease employing conventional vehicles as soon as feasibly possible, as alien-derived craft do not require maintenance fees or fuel. Doing so can considerably reduce your maintenance bills.\\\
You cannot make an enemy of Transtellar, however, as they control all public transit. Civilians like your scientists and engineers require public transports to move from base to base, or to bring new hires to your labs. They cannot use your own vehicles for this, which means you can flip off the police, vaporise the assets of the Megacorps and violently depose the government but God help you if you annoy the [[AlmightyJanitor Taxi drivers]].\\\
Another reason for not making enemies out of everyone is that you'll be tormented with frequent base invasions if you annoy someone too much. This invariably results in the death of a few of your unarmed and unarmoured scientists, as well as being extremely irritating. What this boils down to is: Keep manufacturing equipment with the best profitability margins with your engineers for cash flow; keep raiding companies you don't like for equipment, while making your troops dualwield Devastator cannons and sweeping fire across their maps in real-time combat to make them so poor they cannot afford to raid you... and keep bribing Transtellar to keep their opinion of you maxed out. You can theoretically level the entire city except for Transtellar... including the government and the police.
* ShoutOut: Marsec and the M4000 autogun are a refrence to the early Gollop brothers game, Laser Squad.
* SpareBodyParts: Psimorphs are explained to be so resilient because they have as many as ''twelve'' copies of every major organ.
* TheSyndicate: Three of them.
* TakeOverTheCity: The Aliens' goal is take over Mega-Primus as a first step to taking over the world. Your mission is to invade the alien dimension and to destroy ''their'' city, one building at the time.
* TheWarSequence: The [[TitleDrop Apocalypse]] Mission may be triggered if X-Com completes half the missions in the Alien Dimension: every alien ship in the dimension will go through the gate and start laying waste to the city. Thankfully, this only happens on higher difficulties, and can only occur once per game.
* TeleportersAndTransporters: Personal teleporters in ''Apocalypse''. Aliens appear to 'beam down' to buildings on the Cityscape with some form of white tube effect; not to be mistaken for the ominous blue [[spoiler:Micronoid Rain]].
* TubeTravel: The main form of pedestrian travel in Mega-Primus.
* UniversalPoison: Averted. The first poison deployed by X-COM, "Toxin A", is little effective on aliens and possibly more dangerous to mankind. As research progresses, X-COM develops more specialized toxins that hurt aliens more and humans less.
* UrbanSegregation: Outside of Mega-Primus there are few old, degraded buildings that is all that is left of old Toronto. Hybrids and Androids are forced to live here, while the gangs operate from there.
* UrbanWarfare: Most of the game takes place in one big city, so this is inevitable.
* UterineReplicator: Making babies the old-fashioned way is unpopular by the time of 2084, where they are now grown in Procreation Parks.
* TheVeryDefinitelyFinalDungeon: The alien dimension is an excessively long version of this trope.
* VirtualPaperDoll: You can combine different armor parts, mostly for Marsec Flying Armor torso part, which is the only part required to be able to fly.
* WhatMeasureIsANonHuman: Asked by S.E.L.F. and the Mutant Alliance as they fill X-COM's needs for robotic and [[HalfHumanHybrid alien-hybrid]] soldiers, respectively.
* WeBuyAnything: Strangely not averted. However, apparently [[AdamSmithHatesYourGuts Adam Smith Hates X-COM's Guts]], since market prices for player-manufactured items in ''Apocalypse'' can only go down.
* WeSellEverything: Subverted, as it required you to maintain good relations with a variety of {{Mega Corp}}s to obtain troops, aircraft, weapons, safety from police interference, etc.
* WeirdTradeUnion: The various organizations supply their respective goods and personnel to X-COM. Fail to protect them from aliens or just piss them off, and they will stop making business with you.
[[/folder]]

----
|| '''End Turn''' ||
|| '''HIDDEN MOVEMENT''' ||
->*pew* *pop* *pew* *pop*
->*slither* *slither* *slither* *slither* *slither* *pit* *pat* *pit* *pat*
->'''*BOOM*'''
->[[RedShirt "Aiiieeegurgle gurgle..."]]
->THAT'S X-COM, BABY!
----