Boss Refreshed Wiki & Guide
wiki.9minecraft.net/boss-refreshed-9minecraft-resource-pack/
Guide to the Boss Refreshed pack - how it retextures the Ender Dragon, Wither, Warden and Elder Guardian, its OptiFine CEM models, and how to use it.
Overview
Boss Refreshed is a texture pack that overhauls the look of Minecraft's major bosses. It replaces the artwork of the Ender Dragon, the Wither, the Warden and the Elder Guardian with darker, more detailed designs while keeping each mob instantly recognizable.
The pack only changes textures (and optional models); it adds no items, blocks or mechanics, so it is safe to combine with almost any other pack or setup.