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I Am Watchful I Am Necessary by TheConstellation reviews
Decades have past since the Ethereals threat was defeated and humanity has emerged united and stronger than ever for the conflict it faced. Now after discovering the Prothean Archives on Mars, humanity is about to end up on a much larger stage than it ever expected to play on when yet another alien threat comes knocking. And again, X-COM stands ready to fight. Vigilo Confido.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 9 - Words: 18,569 - Reviews: 344 - Favs: 636 - Follows: 881 - Updated: 2/25 - Published: 9/30/2013 - Admiral Hackett
Vigil by Peptuck reviews
Mankind has survived its crucible, and while scarred and changed by the Ethereals, they advance into the cosmos. The galaxy beyond is a place of wonder and terror, of wealth and strife. Amid the threats and opportunities, both within and without, XCOM remains vigilant. Mass Effect/XCOM/Eclipse Phase/FEAR fusion.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi/Adventure - Chapters: 12 - Words: 112,376 - Reviews: 299 - Favs: 548 - Follows: 617 - Updated: 2/18 - Published: 9/2/2014
Aleandrea's Alien Primer - Combined and Condensed Edition by 5 Coloured Walker reviews
Alien's aren't just people with rubber faces and funny hats.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 2 - Words: 2,189 - Reviews: 2 - Favs: 1 - Follows: 1 - Published: 2/18
Ferris by Jonn Wood reviews
A geek ends up in the XCOM universe. Good News: He's just the Chief Engineer's personal assistant. Bad News: The Chief Engineer is Tony Stark.
Crossover - X-Com & Ironman - Rated: T - English - Sci-Fi/Drama - Chapters: 20 - Words: 80,295 - Reviews: 26 - Favs: 52 - Follows: 74 - Updated: 2/17 - Published: 1/8/2014 - A. E. Stark/Tony
Council's notes on Humanity by 5 Coloured Walker reviews
This is the Citadel Codex as it applies to Humans in the [TBD] world, who's current stories include: Busy Stars This however is not the codex of general things however, not is it human's documentation on aliens.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 2 - Words: 2,321 - Reviews: 1 - Favs: 11 - Follows: 15 - Published: 2/11
X-com percy jackson crossover challenge by themarineguy
This is really just a challenge
Crossover - X-Com & Percy Jackson and the Olympians - Rated: K - English - Chapters: 1 - Words: 222 - Published: 1/31
Psi Effect by Cap'n Chryssalid reviews
A fun-loving asari mercenary finds herself a little in over her head when she ends up abducted by terrifying aliens from beyond the galactic frontier. These asari-like creatures call themselves 'humans.' They seem to be secretly nosing about on the borders of known space, acting through proxies, conducting covert operations, and they've got a deal for an enterprising asari...
Crossover - X-Com & Mass Effect - Rated: T - English - Humor/Sci-Fi - Chapters: 12 - Words: 118,023 - Reviews: 342 - Favs: 1,154 - Follows: 1,426 - Updated: 1/29 - Published: 7/19/2014 - U. Wrex, Daro'Xen, Shepard (F), Shepard (M)
Smoke on the Water by P.H. Wise reviews
Centuries after the Ethereal war, after humanity discovered a galaxy filled with alien life, after the defeat of Sovereign, the abductions have begun again. This time, entire human colonies are disappearing. And a reborn Commander Shepard and the long-thought defunct Extraterrestrial Combat Unit may be the only thing standing between humanity and extinction... (XCOM/Mass Effect)
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 6 - Words: 45,280 - Reviews: 32 - Favs: 109 - Follows: 164 - Updated: 1/20 - Published: 7/19/2014 - Shepard (F), Liara T'Soni, Miranda L.
XCOM: Enemy Monstrous by Malcho1234 reviews
It was over... XCOM defeated the Enemy from the unknown reaches of Space. They eliminated the enemy within... But threats for Humanity still exist, and they are closer than ever, living amongst us... It is time for X-COM's youngest Operative to face the Enemy Monstrous... Rated T because of XCOM. Possible OC/Harem
Crossover - X-Com & Rosario + Vampire - Rated: T - English - Supernatural/Sci-Fi - Chapters: 6 - Words: 17,532 - Reviews: 44 - Favs: 84 - Follows: 77 - Updated: 1/5 - Published: 8/10/2014
Dust and Psionics by Malcho1234 reviews
Tossed in a new world... One full of strange enemies and even stranger humans... And yet, there is one thing that remains the same: Humanity is in danger. And Christopher Redmond had sworn to protect Humanity... Rated T because of XCOM, might take it up to M later.
Crossover - X-Com & RWBY - Rated: T - English - Fantasy/Sci-Fi - Chapters: 5 - Words: 21,678 - Reviews: 53 - Favs: 95 - Follows: 119 - Updated: 1/5 - Published: 10/11/2014 - Ruby Rose, Weiss Schnee, Yang Xiao Long, OC
Stargate: Friends in High places by Jogme111 reviews
The story shows the struggles of SG-1, A team of elite American soldiers, once joined by the mysterious XCOM organization, who is fighting it's own war. New story.
Crossover - Stargate: SG-1 & X-Com - Rated: T - English - Sci-Fi/Adventure - Chapters: 3 - Words: 1,266 - Reviews: 3 - Favs: 2 - Follows: 4 - Updated: 12/25/2014 - Published: 12/16/2014
XCOM: SG-1 by Jogme111
As XCOM fights one extraterrestrial menace, another hides in the shadows. But also another friend. This is a continuation for XCOM: HEROES UNKNOWN. I recommend you go get reading on that short one. It was like the intro and it summarizes the characters.
Crossover - Stargate: SG-1 & X-Com - Rated: T - English - Sci-Fi/Adventure - Chapters: 2 - Words: 1,009 - Favs: 4 - Follows: 4 - Updated: 12/14/2014 - Published: 12/13/2014
XCOM: Heroes Unknown by Jogme111 reviews
The project known as XCOM gets activated to repel an alien invasion. Earth's first and last line of defense. But what they didn't know is that through all these enemies, they would find a friend.
Crossover - Star Wars & X-Com - Rated: T - English - Sci-Fi - Chapters: 4 - Words: 1,995 - Reviews: 2 - Favs: 3 - Follows: 6 - Updated: 12/13/2014 - Published: 11/13/2014 - Complete
X-COM: Silence Within by jak3combat reviews
My name is David Zalian, used to be a Lance Corporal in the USMC. April 1st, 2015, we had official first contact. It... went rather poorly, and I ended up recruited by a group of people only known as X-COM. I have a few suspicions about my new Commander, but I have more pressing things to deal with.
Crossover - X-Com & My Little Pony - Rated: T - English - Sci-Fi - Chapters: 1 - Words: 1,736 - Reviews: 4 - Favs: 7 - Follows: 10 - Published: 12/3/2014
Adapt and Survive by nivlac reviews
It has been two weeks since Rolf Anderson sacrificed his life to save the earth, and during his funeral, a mysterious cloaked man took them and their base from the earth that they worked so hard to save. The base was put on a new, more hostile version of earth, full of mutants, slavers, radiation, and power armored soldiers with laser and plasma technology on par with their own.
Crossover - X-Com & Fallout - Rated: T - English - Tragedy/Mystery - Chapters: 1 - Words: 4,071 - Reviews: 8 - Favs: 10 - Follows: 13 - Updated: 11/30/2014 - Published: 11/27/2014 - Lone Wanderer, Elder Lyons, Fawkes, Colonel Autumn
X-Com Into Darkness by deathwing17 reviews
After an information gathering mission in China, The leaders of X-Com learn that something strange is going on in Japan. They send a team in to investigate only for them to find something more disturbing than they originally feared.
Crossover - X-Com & Brynhildr in the Darkness/極黒のブリュンヒルデ - Rated: T - English - Sci-Fi/Horror - Chapters: 4 - Words: 23,222 - Reviews: 10 - Favs: 17 - Follows: 23 - Updated: 11/19/2014 - Published: 8/12/2014
Justice League: The Enemy and the Unknown by Korgeta reviews
A secret war has been waged for too long and as the league is set to investigate find themselves muddled between ambition, enemies and division of what is to come.
Crossover - X-Com & Justice League - Rated: T - English - Mystery/Drama - Chapters: 1 - Words: 435 - Reviews: 1 - Favs: 2 - Follows: 5 - Published: 11/16/2014
Pony Unknown by DEATHxCHAN reviews
Same idea as in X-COM: Pony Within, just that Twilight manages to get back to her world on her own. But, it wouldn't be interesting if Dr. Vahlen, Dr. Shen and Central Officer Bradford wouldn't get sucked inside the collapsing portal. Oh and I put a lot less effort into this. Sorry ;-)
Crossover - X-Com & My Little Pony - Rated: T - English - Friendship - Chapters: 2 - Words: 5,266 - Reviews: 3 - Favs: 7 - Follows: 7 - Updated: 11/14/2014 - Published: 10/17/2014 - Twilight Sparkle
All terrans by SleeperS reviews
First try. OP-Humanity. Dimensional travel. MY playground. Not sure what it will be... Better description i will add with more chapters.
Crossover - X-Com & Mass Effect - Rated: T - English - Chapters: 2 - Words: 2,302 - Reviews: 7 - Favs: 8 - Follows: 13 - Updated: 10/24/2014 - Published: 10/23/2014
X-COM Pony within by DEATHxCHAN reviews
Bradford, Dr. Vahlen and Dr. Shen learn that their Commander is not what she seems to be. Twilight in the meantime has changed a lot during her 4 years in the human world. That's an excuse for her being OOC, btw. And then her friends appear one after another in the X-COM base, in order to get her back to Equestria. (I don't mind if someone copies this idea) C4 quality down sickness
Crossover - X-Com & My Little Pony - Rated: T - English - Friendship - Chapters: 4 - Words: 15,168 - Reviews: 10 - Favs: 11 - Follows: 19 - Updated: 10/22/2014 - Published: 9/12/2014 - Twilight Sparkle, Pinkie Pie, Spike, Sunset Shimmer
Do you wanna by Korgeta reviews
Basically a song parody of said Title but Xcom themed. A short silly piece from me.
Crossover - X-Com & Frozen - Rated: K+ - English - Humor/Parody - Chapters: 1 - Words: 210 - Reviews: 3 - Favs: 2 - Published: 9/28/2014 - Complete
Jack Slash, Hero of Earth by MortiferSB reviews
The Slaughterhouse Nine wake up in the XCOM universe. This can only end well.
Crossover - X-Com & Worm - Rated: T - English - Adventure/Sci-Fi - Chapters: 2 - Words: 1,923 - Reviews: 25 - Favs: 60 - Follows: 79 - Updated: 9/21/2014 - Published: 7/16/2014
Cause and Effect by Eotyrannus reviews
The Temple Ship threatened to eradicate either XCOM's finest or the entire human race. Instead, it took itself into a whole new universe, where the races of the galaxy used the incredible Element Zero to cross the stars. No one has any idea what's coming... *Being replaced with a remake*
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 7 - Words: 21,235 - Reviews: 62 - Favs: 211 - Follows: 295 - Updated: 9/15/2014 - Published: 5/18/2014
The Technological Assimilators by Knight in Blackest Armor reviews
With the technologies of several alien races at its disposal, humanity had undergone a technological revolution. It advanced at such a rapid pace, far exceeding many expectations. Soon however, the humans learned that they shared their galaxy with yet another group of sentient alien life, but to mankind's horror and confusion, these aliens were not the sort they expected at all.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 4 - Words: 94,510 - Reviews: 152 - Favs: 499 - Follows: 700 - Updated: 8/31/2014 - Published: 3/20/2014
X-COM: Enduring Legacy by Wixeron reviews
Humanity has survived, adapted and won against extraterrestrial threats even before they leave Earth. Now, with a changed mentality, they took to the stars and would bring about a revolution to the galactic community and inadvertently, change the course of the Cycle.
Crossover - X-Com & Mass Effect - Rated: T - English - Sci-Fi - Chapters: 4 - Words: 21,696 - Reviews: 38 - Favs: 137 - Follows: 189 - Updated: 8/23/2014 - Published: 7/27/2014
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