Great Antosha
Since I'm not a modder, it was already an achievement for me to rework the textures for the basic and upgraded versions of the Mermaids.
And I didn't forbid anyone from creating their own fixes for the mod in the archive with the Campaigns. Actually, the core of the mod isn't mine; I didn't delve too deeply into it due to my lack of skill. So, you can rework not only points 3, 4, and 5, but also point 1.
Regarding the second point, I have ideas for a completely different Griffin offspring. However, it doesn't quite fit into the overall storyline yet, and I also need to finally play through the sixth installment properly, not just skim through it, to fully understand the character's personality. Unfortunately, I don't have enough time and energy for all of this right now.
P.S. Following Zakhar's advice, there's a suggestion to completely rearrange the first three tiers, where the 1st level, Kappa, would be followed by the Sharklings as the second, and the Water Spirits as the third.
The thing is, in Heroes V, they wanted to create a Campaign featuring the Nagas, and Oleg Griffin and Cyrus united against the Order of the Void, using Zakira for this purpose. And with this mod, you can now create a fan version of this Campaign! But to understand the character's personality, you can simply watch this gameplay video: https://www.youtube.com/watch?v=2iLESZJKMJY.
In Heroes VI, the Shark Guards are stronger than the Kappa only in terms of health, but in terms of defense and other parameters, the Kappa are already better, so you can leave it as is. Perhaps the Stream Spirits should be on level 5, and the Priestesses on level 3? And for the "four waves," I think Whirlwind is more similar to Kensei than Storm, which only attacks twice, even though the three attacks from the waves can be combined in strength into a second attack, and the Berserker's desire to crush is more similar to Storm? And shouldn't the Kirin be able to fly? In Heroes VI, they followed air currents above the ground...