Tips for fighting undead armies as Franz

First time fighting undead. I just had a succesfull battle and took out vlad and Isabella.

However, I am not sure how exactly to fight undead armies. This is my first campaign fighting them.

Playing VH VH for the first time starting. Finished most of a Tyrion campaign on VH Vh but this is way tougher.

What types of damage are best against different units?

Are magical attacks much better vs the ghostly looking units like scythe infantry?

Are archers just the same vs skeletons?

Guns vs bats and vargheists was effective.

I have a grey (shadows) caster. What spells should I be using vs specific types of units?

It is turn 17.