This is not really a guide, this is about those of you who have no idea how a game works(not just MK, but any other game as well) and how the game communicate with the PC.

The goal of this is to enlighten and help those of you who struggle to understand why the game is stuttering, lagging or just runs on slow motion.
Enjoy....

Let's imagine a 3D virtual model for a second, this 3D model is built from vertices that are usually calculated from your CPU, then there's the polygons, textures and shaders that are calculated by your GPU and your RAM.

Now, Imagine you have 100 of those models at once in your screen...
You starting to get the idea, yeah? :)

Screen resolution is calculated by pixels on the screen, higher resolution = more pixels = more stress for your PC and vise versa. For example...

800x600 = 480000 pixels (less stress)
1920x1080 = 2073600 pixels (more stress)

Lowering the screen resolution when you suffer from bad performance even tho you already put all the details to it's very low values, it's always worth doing.
Just because you set all the ingame details(textures,shadows,models,aa,af,etc) to Low/Off does not mean you have done everything but the game still runs in slow motion...
This is especially recommended for those of you with lower end laptops or desktop systems with integrated or low-end GPU and CPU.
Lower the resolution!

By doing this, you will not only help yourself, but also the others who want to have an enjoyable experience playing against you over the internet.

Here's something else...
Always make sure your software(drivers,windows update,directx) is up to date with the latest revisions and that they are functioning correctly.
You can see all kinds of information about your computer by going into the Device Manager from the Control Panel of each windows platform.
There should not be devices with question or exclamation marks.

If all of the above does not help solve your issues, then I believe it's time for you to consider upgrading your PC.
Just because you run game X with little to no issues, this does not mean you can run this one, and just because your PC was top grade 10 years ago, this does not mean it's also good now.

When you launch the game, the dragon symbol appear but then it just closes and nothing happens?
Simple solution really...
Navigate to you MKKE config folder located in C:\Users\<username>\AppData\Roaming\MKKE
and delete either everything from the folder, or the folder itself.
This will force the game to think that it launches for the first time, and should start properly.
If you can't find the "AppData" folder on your PC, make sure you set your windows to show you the hidden folder.
If you still can't find it, try typing %appdata% in the windows "Run" tool (Winkey+R)

Don't use the ingame "Friend Invite" option. Instead, press Shift+Tab and invite your friend trough the steam overlay. It works flawlessly.

You have modified the options.ini in the MKKE config folder.
Solution: press Windows key+R and paste that: "%appdata%/mkke"(without the "") then delete options.ini

Rumours say that if both players pick randomly there's a 50% chance to get this error.
Or during the loading screen where players put the fight code can get this error.

Other reason according to WB Support is the input controller or keybindings.
With possible solution is to go Options > Controller > Reset to default.

Since the game itself does not support that extra, I found a way to sort a "trick it" to do so.
Without further ado, here's what you need to do.

-Download a tool called "Open Broadcaster"
-Install it and run it AFTER the game launch.

Now... what you basically need to do is to show the tool from which source to stream (In this case MKKE)
On the bottom side of the tool you will see 2(two) small boxes, one is "Scenes" and the other is "Sources".
Don't mess with the "Scenes" unless you really know what are you doing.
Right click inside the "Sources" box and go Add > Game Capture and make sure there's a tick on "Stretch image to screen" option.
This may require you to restart the tool, but don't worry, once you did that just click on "Preview Stream" button at the bottom right hand side while your game is running in the background, and you should be good to go.
This method is tested using game pad and it works flawlessly.
The end result will look like this:
You can resize it, drag it, and pretty much everything you want from a windowed mode.
Njoy, and don't forget to leave a comment and rate that guide so we can help as many people as possible!

There are several reasons why this may occur. I hear reports that this may be caused by using the ingame AA(Antialising) for some reason, or by low populated region(which makes more sense).
Try switching the ingame AA off, and if you still see empty rooms, or really few people, then this is because of the low populated area/region.
To switch to more populated area/region, go to your Steam>Settings>Downloads and where it sais "Download region" select some more highly populated area near you. Also, make sure that "Limit download to the fallowing bandwith" is set to "No limit" and "Game server browser: max pings / minutes" is set to "Automatic (5000)"

Highly populated areas I know:
Russia - Central
Germany - Berlin
US - Dallas

Please let me know in the comments if you know more highly populated areas so I can add them to the list.
Thanks in advance.

I see a lot of people here and in the game complaining about input lag and slow-mo effect while still doing 60fps.
Well, there's a logical explanation for that.
Using some sort of ingame AA(Antialising) auto activates vsync to make it all nice and smooth. The thing is(as some of us may already know) Vsync adds a bit of input lag to eliminate the screan tearing, and it may also cause some slowdowns.
So....
Case 1: You are using some sort of AA ingame, or offgame
Case 2: You are using forced vsync trough CCC, NVCP, or any other 3rd party app.

So there you go, you have 2 options.
Solution 1: Don't use AA and/or forced vsync
Solution 2: Use a 3rd partry app to limit your fps(frames per seconds) to 59, so that way when you use AA and/or vsync you wont have any lags, tearing, or slowdowns.
I prefer "Solution 2"

Update:
I'm hearing reports, that, for some reason AF(Anisotropic Filtering) can hurt the performance really bad.
Try turning this particular settings all the way down to "OFF" or just lower it a bit and see how it works.