I think that units should suffer higher penalties for fighting in wrong terrain type e.g. Giant Scorpion in wetlands has penalty only -10 to pursuit and -20 to toughtnes wich is no much if u look that it has 190dmg after debuf 70 toughtnes and 1 pursuit. I would suggest add -50 to dmg.
That would make playing with monsters more strategic, pulling enemies in to traps and if failed suffer more. Monsters are really strong thought.
The more powerfull unit is the higher penalties should suffer from wrong terrain. Some monsters atm have no pennalties at all. Treants could suffer always out of forests some penalties if we look at huge buff in it.
Just my thoughts. I think You did great job.

Every cavalery units types e.g. Wargs should suffer in mountains..

Ah damn just answered you in the mod comments, here would've been better. Oh well.
Anyway, about your last point: I see what you mean, the thing is just that in my mind wargs, unlike horses, are pretty agile, so they wouldn't really have the same problems, especially since they have no riders.
Warg cavalry I definitely would penalize in mountains.
That's one of the biggest issues I have, I realize that everyone has different perceptions of fantasy creatures and I will not be able to satisfy everyone.

One solution would be to add smaller penalties in such cases, but this could easily lead to an overcrowded UI. Not too many people want to read through 10 terrain boni/mali to figure out how to properly use the unit. Still, as I mentioned in my other comment, I will keep it in mind in the future.

I see your points. As I said u did great job with this mod keep it up ;)