OPTIFINE IS NEEDED!To get multiple textures for one mob, is more complicated than you may think, but if you pay attention, you should understand.
1: Make sure you have optifine or mcpatcher. If you do not have one of those it will not work.
2: Open your resource pack folder.
3: Open the pack you want than click assets.
You should now see a Minecraft folder, go ahead and open that.
4: Now, You should be in a folder that has different folders in it such as Textures. Look for one that says “mcpatcher”. If you do not have one with that name, create one by Right clicking an empty spot, go go to “New” and click “folder”. Now you should have a folder named “New Folder”. Now you want to double click it and delete “New folder” and put “mcpatcher”. Even if you are using optifine!
5: Now open that folder. If you already had that folder, you should have a folder called “mob” If not, create one just how we did in the other step. Once you have a mob folder open it.
6: So in the mod folder, you can create a folder or any type of mob you want to have multiple textures for. So if you want a ton of dog textures make a folder called “wolf”
7: The next step is important. You put the texture of the mob in this folder with .png at the end. So if I add a Wolf texture it would be wolf.png. And if you add multiple, you would add a number at the end. So another wolf would be “wolf2.png” then “wolf3.png” Also, with the wolf, there are three textures for it. There is wolf.png, wolf_tame.png, and wolf_angry.png. You will need to have a texture for each one.
8: the last step is Easy. Go into you minecraft Options, Then go to Video settings, than Quality, And on the left side, there is a thing thats says “Random Mobs” Turn that on otherwise it will not work. After all of that you are done