By the way, has anyone already made a necromancer mod... in which plague ents are raised from all ents and dendroids!

Yes, but it's for the original game. And in my opinion, they are too overpowered there.
I will only take textures from there.

Here, the problem will be different... there is only one yeti.
Most likely, I will have to sacrifice the black knights, which are also unused. BUT on the other hand, I have an idea to raise all black knight riders, and make death knights an upgrade, as it should be in the game originally.

In any case, I will need plague ents when I create a map about the conquest of Erathia. Although, if I make a campaign, I might need to connect the NCF core as well.

Added 1 minute ago

Why make such a mage if there are already many shadow creatures in the game: liches, dusk witches?

I agree. I want to give combat mages the ability to summon elementals.