Sorry for the question, but is the list being compiled based on the world of Ashan? If so, unicorns could be made into mounts for elven heroes, and pegasi could be assigned to the Free Cities.
The list is being compiled based on the canonical nature of the troops and the world of Ashan. Mostly creatures from the third and fifth games.

I want to add that I'm not writing about, for example, a specific Urgash creature, but rather a creature of pure fire. Or instead of an Elrat creature, I'm writing about a creature of pure light. Do you understand?

Added 2 minutes later

1. Assassin / Beast / Stalker / Troglodyte (as a last resort)
2. Contemplator
3. Minotaur
4. Manticore
5. Faceless / Twilight Witch
6. Hydra
7. Dragon

This is the optimal version of this Faction, in my opinion.

Almost. An assassin is on the first level, but it's the one that doesn't shoot, but the one that hides (like in the sixth game).
The hydra has been replaced with lizard riders and they have been moved to the 3rd level. I don't know how to bring the hydra back yet. For me, it's a swamp creature, not an underground one.