So I discovered a very cheesy way of winning battles with the human towns. Just take Imperial griffins and nothing else and use their Battle Dive till you kill everyone (with the griffins gone, the enemies can't do anything and just stand there). How was this not caught and fixed (like by not allowing Battle Dive if no other creatures are present), given how many people play this game, including multiplayer where it could be easily abused?

The player waiting for them to come back can do things, including moving the target out of the way (or all of your units, if you don't know the target) and hitting the griffins while they wait for their next turn. Manipulate the initiative order to set up to damage the griffins.

OK, that makes sense. It seems to be abusable vs the AI though.

It might be abusable; I haven't played in awhile and I don't remember the fine details. I do remember being somewhat unimpressed by battle dive, overall. Sure, the griffins can't be hit, but I recall it being slower to finish (so your griffins aren't helping your other units deal damage, block, or what-have-you), the dive targets a square (not a unit) so it can be avoided, their battlefield position after the dive seems random, and the griffins can be pounded on while waiting for their next turn so they can dive again (and they aren't the sturdiest creatures in the first place). Battle diving will NOT win you a battle against a decent enemy force.

You do see one pseudo-exploit using Battledive in one of the Human campaign missions, though! Granted, it is a somewhat scripted AI v AI battle, but still.

The exploit can be mainly useful against single stacks of slow monsters (without heroes). Just battle dive, rinse and repeat.
I just stumbled across it accidentally and I haven't used it so I haven't really experimented with it.

I find Battle Dive quite useful, especially if you get initiative/morale boosts vs slow or ranged units. If you see the griffins appearing twice before the enemies turn, you know that unit won't get a chance to move. Or against ranged units (if they move, they waste their attack so it's good anyway). Been also very helpful vs pit lords with their fireball casting (if they move, it means they didn't cast the fireball and did less damage, if they cast the fireball, they don't move and the griffins get them. Which one? I have finished human campaigned and don't recall seeing it.

Oh! Well, that's an entirely different matter, and yes, battle dive is great if you can line up the consecutive turns and none of your stuff is at risk. I thought you were talking about using it against AI heroes with multi-stack armies. I had to look it up. You'll see the battle in the 5th Haven mission. You literally can't miss it; my mother managed to circumvent the battle when she was playing, and then she couldn't complete the map. XD

I literally finished that level today. Don't think I saw it.
Are you talking about the original campaign (not Hammers of Fate or Tribes of the East), level called The Fall of the King? If so, which battle is it?

Yes, Fall of the King. Nicolai runs out and gets in a fight with a demon hero. His forces are taking a beating, then the griffins battle dive and he casts Armageddon while they're in the air. The enemy forces are savaged, but Nicolai is overrun shortly after that.

My mother reloaded to a point before that battle and positioned her hero to knock out the demon hero before Nicolai could get killed. She wasn't able to finish the map after beating the demon hero.

Just replayed it. I'm not seeing griffins when Nicolai casts Armageddon. This is all I see:
https://youtu.be/dWzi_zu2qxk?t=1402

Huh. I just checked a walkthrough for the mission, and the walkthrough didn't show the battle at all, just that cut scene you linked. I could have sword there was an AI v AI battle which Nicolai lost. Maybe it was changed in a patch, or I'm conflating two different events.

Aaah, I believe I got it. You're confusing it with the intro of the first level of that campaign when Nicolai fights the demon army
https://youtu.be/dWzi_zu2qxk?t=280

Ah ha! Good call. I remembered angels being present, Nicolai's forces taking a beating, and Nicolai blowing up the battle field before the griffins came down. I just couldn't remember exactly where it happened. I thought it showed more of the battlefield, and wasn't quite as cut-scene-y, but it has been several years since I last played.

I definitely remember the bit about the 5th map, because I had a good laugh when my mother told me about it.

Sorry to bump this, but I just found out something weird.

I was having trouble battling some archmages because of their spells and me wanting a lossless battle, so I tried attacking with battle griffins only.

Something very weird happened. My griffins did a battle dive and soon as they disappeared the archmages (3 stacks of them) started... casting fireballs on themselves.
They'd either cast it at themselves, or at one of the other archmage stacks. Once the griffins got down, the archmages proceeded to attack the griffins, until those disappear again.

Looks like whoever worked on the algorithm of choosing spell target for archmages forgot to add that if no enemy target exists for fireball they should do something else instead.

That's hilarious, and somehow unsurprising. XD

Also happened when attacking Elder Druids. Seems to be a common AI bug for all spellcasters.

I just started the Hammers of Fate expansion and the campaign seems to suffer from the same issue as the original: no "proper" classic strategy levels: one where you build/capture cities instead of the pseudo-RPGesque ones.

I've played only 2 levels so hopefully this will change.