The Mobs folder includes 2 - 6 varients of most mobs.
The mobs that have 2 varients or 4, you can find the rest in the FarnRandomMob folder. 

For these textures to work use Farn's Random Mob Texture Mod: 

https://github.com/FarnGitHub/Farn-s-Random-Mob/releases/tag/2.0-Unimined-RTM-A126

If you are using a skinfix and want to see your skin use this instead:

https://github.com/FarnGitHub/Farn-s-Random-Mob/releases/tag/2.0.1-Unimined-a126

^^^^^^
Requires JarModAgent to work properly

https://github.com/FarnGitHub/Farn_Minecraft_Mod_Collection/wiki/Unimined-JarModAgent-Installation


You can choose to rename one of the varients if you like it, 
just delete the png that does not have a number and rename - 
one of the other png's to not have a number!

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For alpha grass and foliage:

Rename terrain_alt.png to terrain.png and go to "misc/alt" folder and read the README.txt for instructions

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For the files named 
"Custom_[BLANK].png"
These require a version of MCPatcher mods
for them to be used ingame.