NHF – new heroes for Heroes V 3.1.

If only some, then this is an NCF bug, specifically related to those creatures in the project.

Regarding Ilmirn, I would like the growth to also be tied to the hero's level.

So far, all the new alt-upgrade units I've encountered (gremlins with area-of-effect attacks and spear throwers in golden armor) haven't been turned into a necromantic army.

Make it as ingenious as with other hero-oriented creatures: levels 1-9 -> 1 returns; levels 10+ -> 2.

Kostya has already gained the ability to dress volunteers in necromantic form without extra effort (transformation happens on the spot). And even once, 47 dwarves voluntarily became skeletons.