Mine Little Pony requires the mod loader LiteLoader in order to run. Download the Mine Little Pony mod and the LiteLoader installer for Minecraft 1.8.0 from the front page.
Download the appropriate installer for your operating system: download the .EXE installer if you are using WIndows and .JAR for other operating systems. Open the installer and follow the on screen instructions.
The Mine Little Pony mod should have a .LITEMOD extension. Place the .LITEMOD file in the "mods" folder that has been created in your "minecraft" root folder.
If everything was done correctly, a new Minecraft profile named "LiteLoader 1.11.2" should appear in the drop down menu. Choose that profile and launch the game and you're done! Congratulations on your newfound poniness!