How often do you come across mob heads in Minecraft? I don't know, but I sure do remember what they used to look like and made them that! (I mean, you see them a lot in servers' UIs—)

Better yet, in three different variations, so everyone can pick!

Dynamic (modern solution)

There's the 'Dynamic' variant which simulates the appearance in GUIs while maintaining the modern functionality! (of applying players' skins, other packs' textures):

Fully flat

And obviously there're the variants that bring back the old look fully, comparison of which you can see up ahead:

*_If you do use this in a pack of your own, please mention me_