Custom Entity Models (CEM)

It can be done without optifine!

The Ancient Hovering Inferno by ShadowsCrow

Another proof of concept! Download it here: https://www.planetminecraft.com/texture-pack/the-ancient-hovering-inferno/

Creeper Skele by Supamegabread

Proof of concept! Download it here: https://www.planetminecraft.com/texture-pack/creeper-skeleton-thingy/