Here I will tell you how to fix the two major bugs in Mythos, the Crash-to-Desktop and how everyone is wearing eyepatches and masks.

How to fix the Crash:

1. Find the Mythos folder in documents/Paradoxinteractive/CK2/Mod.
2. Copy it and the "Mythos.mod" file into wherever you like.
3. Extract everything, because you can't edit a zipped file.
4. Find "static_modifiers.txt" in mythos/Common.
5. Now find the base (vanilla) "static_modifiers.txt" file in programfilesx86/steam/steamapps/common/CrusaderKingsII/common
6. Open both .txt files.
7. Near the bottom of the vanilla one there should be code for hospital, right under fort.
8. Copy that code and put it in the same place in the Mythos one. (Make sure it's in the same place, under fort and above Culture Modifiers or it may break worse).
9. Close both. Save the Mythos one, don't save the vanilla one as you don't want that edited at all.
10. Now change the name of the edited Mythos grand folder (the one called Mythos) to whatever you want. Do the same to the .mod file, but make sure both names are the same. For example: "Mythosfix" and "Mythosfix.mod"
11. Edit the .mod file so that instead of saying "archive=mod/mythos.zip" it should say "path=mod/Mythosfix" (Mythosfix or whatever you named the new Mythos folder). Also, change the name after "name=" to whatever you want, or else you'll have two mods with the same name when you're selecting a mod.
12. Save your edited Mythos files.
13. Place both your edited Mythos file and your edited .mod file into CK2/Mod (Where you found the original Mythos file).
14. Start up the game and select your edited Mythos file.
15. Play.

Now here's the Mask Glitch:
1. Do steps 1-3 from the first fix if you haven't already.
2. Find "portrait_properties.txt" in the "Interface" folder for both CK2 vanilla and Mythos.
3. Copy anything below AND including the line "# p12 mask for the disfigured" in CK2 vanilla's "portrait_properties.txt" and place it in the same spot in the "portrait_properties.txt" for Mythos.
4. Save your Mythos "portrait_properties"
5. Do steps 10-15 from the first fix if you still haven't.

Note: This is for 2.6.2. Later patches may break it again.
Also, don't upload your edited file unless Stanley Yelnats or Kroolx gives you permission. They still technically own the mod, even if they aren't updating it.