WARNING

Only try this mod if you want to take the risk.

This mod is fairly old and it seems several people are experiencing glitches with it. Xian's specter skill is making some people totally invisible to zombies, and loot seems bugged after going beyond level 60. 

Summary

This mod increases the level cap from 60 to 100, incorporates proper health increases, buffs many skills for Xian and Perna to make them actually useful, and adds several quality of life changes to make the game much more enjoyable. 

New in Version 1.1 (3 February 2019)

- Fixed a bug where going in even 1 point into Xian's "Spectre" skill would make you completely invisible to all enemies.

Installation

METHOD 1 (EASY)
Included in the .zip file is 1 file called "Data0.pak". That file needs to be placed in your game's DIDE\DI folder. Overwrite the vanilla "Data0.pak" file.

METHOD 2 (HARD)
For those who want a more manual install that allows 2 or more mods to be merged:

1.) Download my "skills.zip" folder
2.) Extract "data" folder within "Data0.pak"
3.) Navigate through the extracted "data" folder to find the "skills" folder, and overwrite that one with the one you download here
4.) Install all the other mods using your newly extracted "data" folder by overwriting
5.) Once all the mods you want are installed into that "data" folder, compress it (renaming it to "Data0.pak") using ZipCrypto encryption method (using 7-zip)
6.) Navigate to your game's installation folder and within that overwrite the vanilla "Data0.pak" with your new "Data0.pak"

Details

All details are included (in detail) in the optional .zip open office spreadsheet file called "Dead Island Mod DEC 2018.ods", but I'll give a decent rundown here:

default_levels.xml    |    these changes apply to all player-characters (with a focus on realism)

• Reduced stamina cost from jumping
• Increased jump height
• Increased sprint speed
• Increased speed when moving backward
• Increased speed when strafing
• Decreased stamina cost from sprinting
• Increased FOV (from 62.5 to 72.0)
• Increased speed when crouching forward, backward, and strafing
• Increased the duration that damage resistance lasts after death
• Increased the speed you move when carrying things
  

logan_levels.xml

• Increased level cap from 60 to 100
  

(used vanilla formula to calculate experience requirements past level 59)

• Incorporated max health increases on every 5th level after level 20 (25, 30, 35, 40, etc...) 
  

perna_levels.xml

• Increased level cap from 60 to 100
  

(used vanilla formula to calculate experience requirements past level 59)

• Incorporated max health increases on every 5th level after level 20 (25, 30, 35, 40, etc...) 
  

perna_skills.xml

• Weapon damages and durability values have been increased
• Auras have greater effective ranges
• Much more
  

samb_levels.xml

• Increased level cap from 60 to 100
  

(used vanilla formula to calculate experience requirements past level 59)

• Incorporated max health increases on every 5th level after level 20 (25, 30, 35, 40, etc...) 
  

xian_levels.xml

• Increased level cap from 60 to 100
  

(used vanilla formula to calculate experience requirements past level 59)

• Incorporated max health increases on every 5th level after level 20 (25, 30, 35, 40, etc...) 
  

xian_skills.xml

• Weapon damages and durability values have been increased
• Much more
  

Compatibility

I made this mod for the Definitive Edition. I have no idea if it will work for the regular version.

Any mod that changes anything in the "Data0.pak" file will not be compatible with this mod. Everything else is good to go. For reference, only one folder inside Data0.pak has modifications in it: data\skills.

Permissions

Anyone may take what I have done, tailor it to their own tastes, and re-upload anywhere. I require no credit to be given.