MOD: Armageddon's Blade

I had a similar idea, but instead of mind control/blindness/berserk, I thought about creating extra-expert spells of darkness/light, for example, a destructive beam that reduces armor by -50, eternal plague, or weakness that reduces attack by -50.

Added 4 minutes ago
I wanted to give these spells to a Lich, who would be on Tier 7.

Could you provide more details about the spells? How did you achieve these effects and/or modify the unit's magic? (Or is this still a theoretical project?)

Added 7 minutes ago

You'll need to assign 5 different IDs to the creatures; essentially, each upgrade is a different creature. Creating a new skin for each level would be too much; if there were a huge team, it could be done, but as it is, at most, you could modify one model and add an effect (I even know of a cool one with bats). And you could display the levels on the creature's icon using Roman numerals.
I don't know how it would work because I've never given creatures mind control, vampirism, or blindness.
And all the stats and prices are also made up out of thin air.

How do you like this flight of fancy? 😄

Regarding spells for creatures, everything works fine, and in some cases, it's even very interesting! For example, with summoning magic.
1) Creatures have their own spells and a defined spell mastery, so there are no problems for the game – everything works.
2) In some cases, the game doesn't take this into account, and this creates new features. For example, in summoning magic, when I replaced the spells of Archmages and gave them Summon Elementals. And what do you think? Each squad of Archmages could summon their own stack of Elementals, and they didn't conflict with the Hero's Elementals. That is, in this regard, the game considered them all as a separate "Hero," and there was a separate counter for each.
Therefore, in the case of spells that have a limit of one simultaneous target (and mind control should be included here), adding them to creatures can have very "interesting" consequences!

Added 7 minutes ago
Your idea is very interesting; at first, it reminded me of Disciples, and I also remember that in Heroes 3, there were Squires (it was a mod).
But if you want to integrate it into the gameplay and balance, the Disciples variant would look better – namely, something like a "City Guard" or even a Capital Guard – hello, Capitol!
This would strengthen the defense and protect against a rush from a Necromancer/pawn, especially if the unit has a simple but massive spell, like Unholy/Holy Word. Armageddon (with built-in fire immunity). It's very scary at the start, but later it's not dangerous, and in the late game, because the creature is only one, it's not even noticeable!
*An alternative could be adding an area-of-effect ranged attack that covers all enemy units and machines, possibly in conjunction with good initiative. The AoE is feasible; I did it with Destroyers (a replacement for Temptresses). And the damage and other stats/abilities are up to the balance.
Another advantage of this method is that the Guard will receive good bonuses from a strong hero in the city and, conversely, will be weak against a strong enemy hero if your hero is weak or absent.