This has been discussed in earlier topics, but in this thread I present you my idea of how a mix of the two titles could be like, if they were to collide.
Please be patient and read this through before posting your thoughts and oppinions about it, thank you.

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With the MK VS DCU coming up, I have been stirring around some VS games on my own. Some games which I think MK would be better mixing with, since I am not a fan of the DC comics. I would rather see them mix with Marvel, but that’s a whole other story...
Two games who I have wanted to see mixed together for ages now is Killer Instinct, one of my favourite fighting games alongside with the MK series. They have some aspects which look alike, but are different from each other enough to make the series unique. Both of the series are bloody and dark with a mix of humans and mythic races of other worlds.
Killer Instinct was created by Rare alongside Midway, but the rights was bought by Microsoft and since then there have been nothing new about any sequels. Fans like me can only hope that Killer Instinct will be revived, but the future does not look bright, and therefore I would like to see a VS game like this idea I am presenting you here.

For you who do not know the Killer Instinct series, here is a short description of the KI series’ storyline:
-Prequel:
In ages forgotten, two warlords fought each other in an epic battle, the two of them known as Eyedol and Gargos. The war went on for many years, but ended with the two warlords facing each other. The magicks they used opened the portal to Limbo which they were banished to and was forced to wander in eternity.
-Killer Instinct:
Many years after in a near future, a huge corporation known as UltraTech rises above the others. They deal with weapons, both creating and selling. This includes advanced technology, bio-chemical warfare and experimenting with gene-therapy. They have created various humanoid weapons such as the cyborg Fulgore, the lizardman Raptor and the living skeleton Spinal. To test these weapons they created the tournament known as Killer Instinct in which combatants from all over the world has come and test their skills against UltraTech’s own creations.
Just before the newest Killer Instinct tournament, UltraTech have found a way to open portals to other worlds and planes, and found their way to the plane of Limbo where they brought out the mutated form of Eyedol, weakened from the time he wandered in Limbo. UltraTech experimented with him and forced him to fight for them in the upcoming tournament.
-Killer Instinct 2:
Orchid defeated Eyedol which opened the portal to Limbo anew, as the plane craved Eyedol’s soul to return. This opportunity was eyed by Gargos who fled the plane as Eyedol returned to it. Somehow this made UltraTech’s portal-technology go berserk and took the whole HQ back in time to the age where the two warlords had just been banished. Gargos sought to gain power to reign once more, but the combatants of the KI tournament allied with the warriors of the past and cast Gargos back to Limbo while UltraTech tries to return to their own age.
How it ended was never revealed...

MK VS KI storyline:
I do not wish for MK VS KI to be canon to the actual storylines of either series, but the character storylines will of course have aspects of their respective backgrounds. As other VS games, such as Capcom VS SNK and X-Men VS Street Fighter (to mention a few), the game will be non-canon and the storyline will be more like “what if”. The endings will also have aspects of previous titles’ endings with the twist of the colliding of the MK world with the KI world.

Characters...
Because of KI being short on characters comparing to MK, all of them are appearing in the game, though only a matching number of 15 from the MK series will appear.

Killer Instinct:
The Killer Instinct series only have a total of 15 character appearances. This means that all of them will appear in this game.
-Jago: A Tibetan warrior monk who calls on the power of the tiger.
-Fulgore: A prototype cybernetic soldier developed by UltraTech.
-Orchid: A secret agent, her true identity is shrouded in secrecy.
-Combo: Previously a heavy weight boxer champion, his title was stripped from him when found to be using cybernetically enhanced arms.
-Glacius: An alien being from a distant planet, crash landed on Earth.
-Sabrewulf: A man who is afflicted with the disease Lycanthropy.
-Thunder: Mystical defender of Native Americans.
-Cinder: A convict who was experimented on by UltraTech. A failed chemical weapon test mutated his body turning him into a living flame.
-Riptor: A product of UltraTech's DNA manipulation project.
-Spinal: An unprecedented discovery in cell regeneration. UltraTech has recreated an ancient warrior from the past.
-Kim Wu: Descendant of great heroes and Guardian by birth of her home nation.
-Tusk: Champion of a barbarian tribe of the North.
-Maya: Queen of the land of Amazonia.
-Eyedol: Once a warlord who fought a war against Gargos, he was banished to Limbo only to be returned and captured by UltraTech who forced him to fight for them.
-Gargos: Like Eyedol, he was once a warlord who fought a war against him, but was banished to Limbo. He escaped Limbo under certain events in the previous KI series.

Mortal Kombat:
The Killer Instinct series have a wide selection of characters, but 15 characters will appear in this game, matching the 15 characters of the KI series. Though this is regrettably and many popular fan favourites will not appear, I have decided to take some of the top favourites and those who should be expected to appear in such a game as this.
-Sub Zero: Leader of the Lin Kuei clan and a descendant of the Cryomancers.
-Scorpion: A ninja spectre with a vengeful soul.
-Kitana: The princess of Edenia who once was an assassin working for Shao Kahn.
-Kung Lao: A warrior monk of the White Lotus Society.
-Baraka: A Tarkatan warrior who hungers for battle.
-Sonya: The leader of the Outer World Investigation Agency.
-Jax: Sonya’s next-in-command who has cybernetically enhanced arms.
-Kenshi: A blind swordsman who uses telekinesis.
-Raiden: The God of Thunder.
-Sektor: The leader of a clan of cyborgs called the Tekunin.
-Reptile: The last male survivor of the Saurians.
-Kano: Once the leader of the Black Dragon Clan he now works for Shao Kahn.
-Mileena: Clone of Kitana, she is a master of assassination and hides her Tarkatan genes with a veil.
-Goro: The prince of the Shokan race who is a general of Shao Kahn’s army.
-Shao Kahn: The emperor of Outworld.

Gameplay...
I have tried to mix some of the gameplay aspects of MK and KI, so it can work together. Luckily, both series have some aspects which look much alike while other things are entirely different from each other, but I have taken the most popular aspects and put them in this game idea, hoping to make it sound believable and interesting.

Combat system:
All characters will have their unique set of moves, looking much like the previous KI series. While the previous MK series was heavily based of real life martial arts style of combat, it will not appear heavily in this game, though some of the moves will be recognizable.
In previous titles, the KI characters are a mix of fist fighters and weapon wielders while the MK characters could switch between a martial art style and a weapon style. In this game, the KI characters will keep their respective styles, adding some new moves. Some of the MK characters will be all martial arts and others will be all weapon fighting while a few will mix the two styles. For example, Kitana is famous for her Steel Fan weapon fighting and will therefore use her fans as her main style. Scorpion on the other hand will act much like Jago, using his martial art as his main style, but can pull out his blade and spear in a few moves. A fighter like Jax will be all martial art style.

Special Moves:
All characters will have all their special moves from previous titles, and some will even have a few new moves added to their display. This will especially be considered amongst some MK characters, since they have only had very few special moves, e.g. Mileena who only have 3 special moves in the previous MK titles will gain some more moves.

Combo-system:
Killer Instinct was known for its combo-system. The combo-system will return, each character having their own sets of various openings, stylish moves and combo finishers. The Killer Instinct characters will have returning combos from the previous KI titles while the Mortal Kombat characters will be new to this system.

Fatalities:
Mortal Kombat was known for its fatalities which also appeared in Killer Instinct to some extend. These will of course also appear in the game, both returning finisher known from the previous series, but also all new ones for each character.

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Please feel free to post your thoughts and oppinions about this idea, and if you have ideas of your own or something to add, feel free to post those as well.

As a final note, I am aware that this idea would not come true, but the whole idea with this thread was to present my thoughts and ideas to you. Y'know, just for fun!
Enjoy.