There should be a chance of encountering a wild SEM on maps as well.

Agree this would be very cool, but since I don't see it happening I wonder if it is possible for a mod to add a random chance third faction to battles, with wild animals that would attack both sides.

That'd be neat.
I'd also like Peasants who may or may not join the fight in Sieges like.......Was it Rome 2 or Atilla, I forget.

I mean, this would fit in nicely with an idea that's been in my head for a while, something I've called "environmental hazards"

TLDR: certain maps have a chance of something happening, like a river overflowing, a volcano exploding, a herd of BM appearing from the forest and attacking both sides, your idea for a random mammoth herd...

It would make people keep an eye not only on the enemy itself, but also on the map, while also giving new life to old maps.

Mind you, not all maps would have this, but a good chunk could be done.

Rivers impassable except by ford or bridge, habitable buildings like ruined forts/watchtowers, weather actually doing something... I appreciate everything has been reduced in scope from previous Total wars to help the AI and we now have more factors to consider than historical entries but by sigmar battles could be so much more interesting.