We all remember the scene from The Day Of The Doctor, where Tennant is accusing Queen Elizabeth of being a Zygon but, to both of their surprise, the Zygon was actually the Horse that they both rode out of the TARDIS.

My suggestion is to make the Zygon mob able to shape shift into any and all mobs, not just villagers.

we could see Zygon horses, cows, sheep...

Iron golems, Slimes, creepers (and other hostile mobs)...

it could even transform into other Dalek Mod mobs like, a Zygon Cyberman, or a Zygon Dalek

Admittedly, a Zygon Dalek might be a little OP...

By doing this, we could see more Zygons around the world (both DMU and singleplayer worlds). Making Zygon Tongue easy to come by, and thus, making it way easier to craft the glorious dish that is... Zygon Tongue Stew 

From an actual Lore perspective, it would make this alien more resource accurate. Yes, the Zygon's mostly imitated humans in the show, but as evidenced by The Tennant, the Queen and the Horse situation,  Zygons can be any living creature. Plus, it would be kinda cool to reenact the scene where Tennant interrogates a rabbit in case its a Zygon. I feel like that would be a real possible when exploring Minecraft 

Its like...

you explore > you see a sheep > that's good, you need wool to make a bed > you in chat, "Wait, are you a Zygon? > you in chat, "Can I even sheer a Zygon? > *Sheers the "sheep"* > *Sheep turns into a Zygon* > you in chat, "OH HOLY MARY, MOTHER OF GOD!" > *Minecraft Death Screen*

XD

Side Suggestion:

Could you make the Zygons work with Resource Pack?

Because, when I'm exploring villages, its super easy to tell who the Zygon's are. They look like vanilla villagers when my Resource pack makes villagers look very different, it takes the effort out of Zygon hunting.

I suppose I could just disable my resource packs, but I'd rather have obvious Zygons that do that

nice suggestion

Maybe Zygons spawn anywhere in the overworld frequently and kill the nearest mob, then become it?

That is nice or you could come across those zygon chamber things that could generate randomly

Yeah and some have villagers in like in zygon invasion/zygon inversion

and control centres which have a stasis cube in an item frame (day of the doctor)