O
Despite the fact that xel complains in almost every post about how good things were in the good old days for us veterans and how bad it is to play the popular fifth installment, but reading all these ideas... an electric Castle... Baba Yaga... elf-werewolves... he's right. It really is a mess...
Well, okay.
Regarding this idea, which is unlikely to be implemented – why are there any pictures then? Is it criticism? Well, okay. Illithids somehow don't fit with "Heroes." Since we're talking about them, as well as about an enemy, come up with a Castle that will fight them...
The kobolds made me smile :) The un-nerfed ability is fiery, and they also have a torch on their backs, like Mipo and co. But to make them even more similar, don't give them a pickaxe, but a shovel.
The hero shouldn't ride any lizards, spiders, or worms; he should move on his own. My eyes are already tired of these endless mounts. Inferna runs on foot, and that's healthier.
Or, yes, let them levitate... or teleport, if all else fails-_- I mean, teleport across the map, not to some other place.
I think harpies will be fine without a return ability. There are already furies, and giving another unit a return ability, even if it's incomplete, is stupid.
Behemoths (it's better than "monsters") shouldn't be replaced with any rusty/rotten/homeless dragons. It's not the time for dragons. There are already enough of them, and I completely agree with that.
And the racial ability could be something like the gnome (orc) ability - their own guild, where there are "Elite Underground Spellcasters," for example, with darkness on some part of the battlefield, where their own units are invisible like scouts, and enemy archers don't shoot; redirection of buffs/debuffs; and, of course, mind control - hypnosis; maybe "instilling hatred," so that one unit has hatred for another, and will deal increased damage, like djinns to ifrits in the third game; in general, there are many things that can be invented. For the most overpowered spellcasters, if there are any, there could be huge mana costs to maintain balance.
And here's another idea for the racial ability itself. Even if we don't create a separate guild. For example, "enslavement" - a racial spell that is given to every hero from the first level; you cast it on a creature in battle, and it becomes yours. That is, permanently. If it survives the battle, you can take it into your army. Again, you can make the mana cost huge or make taking control dependent on the hero's magic power/knowledge/level, for the sake of balance. In the worst case, it could be an analogue of dark necromantic energy. One of the related abilities is the removal of the negative spirit from mixing creatures from different factions.
It's a pity that, judging by your words, all this will remain only a dream, shrouded in a haze...