Format:
In the custom folder of a texture pack/resource pack there is a herobrine.png or something. Skin the mob with that. That'll prevent so many MM users from trying to buy tons of cracked/illegal accounts and secure them to custom skin their mobs. It'd be awesome, and this is not a method to replace Lib's Disguise, rather just an alternative way so both options are there.
Code:
- disguise{d=custom.herobrine} @self