Replace the Diablos (the normal one) with a black variant, with red veins, also known as a Bloodbath Diablos.

Replace Diablos’ armors, both male and female, alpha and beta.
You can choose to replace the normal Diablos, or the Black Diablos. Simply Download the file corresponding to your choice.

Replace Diablos’ weapons (of Black Diablos' weapons depending on the weapon tree) 
When weapons are composed of a bone base with Diablos partson it, only the Diablos bits are modified.

Optional file to replace bone part of Diablos' weapons with iron parts, more on parts with the bloodbath diablos colors. Note: This will
also affects some other weapons (the ones using the same parts.

Optional file to replace the Samurai Layer armor withBloodbath Diablos' armors, both male and female.

Install: Extract the content of the archive inside the"nativePC" folder (in your game folder 
...\steamapps\common\Monster Hunter World\nativePC).

Note: If you have already installed the mod, but you want to switch from the normal Diablos to the black Diablos (or the other way around), you may want to delete the first version(or both normal and black Diablos will appear as Bloodbath). If you are not using any other texture mods, simply delete your nativePC folder. If you are using other mods, here are the folders to delete.
For the normal Diablos:
F:\Steam\steamapps\common\Monster Hunter World\nativePC\em\em007\00
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\f_equip\pl034_0000
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\f_equip\pl034_0010
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\m_equip\pl034_0000
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\m_equip\pl034_0010

For the black Diablos:
F:\Steam\steamapps\common\Monster Hunter World\nativePC\em\em007\01
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\f_equip\pl034_0100
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\f_equip\pl034_0110
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\m_equip\pl034_0100
F:\Steam\steamapps\common\Monster Hunter World\nativePC\pl\m_equip\pl034_0110