Display textures for Boss/Elite/Rare/RareElite on ElvUI and Shadowed Unit Frames.
Backported to patch 3.3.5 from https://legacy.curseforge.com/wow/addons/simplerareelite.
Clone the repository or download it as a zip file.
git clone https://github.com/tnordenmark/SimpleRareElite.git
If you downloaded the repository as a zip file, extract it and rename the folder from SimpleRareElite-master to SimpleRareElite.
Copy or move the SimpleRareElite folder to <WoW Folder>\Interface\AddOns\.
Restart the game.