Texture Pack for a Modpack

I've made a mod with a custom mob, and I would like to create a texture pack to go with it. My goal is for the texture pack to randomize the texture of this custom mob from a handful of textures i have made for it (think minecraft cats where they have a random texture when spawned). I want the texture pack so that I don't need to have a bunch of different spawn eggs for each different skin. I'm unsure how to go about doing this and I've tried a handful of ways but failed. I'd love some help!