Auto-translated
When it comes to Orcs, I find the battles between Garuna and Ravenna, Hellmar, and Vitto interesting. In the first one, resistance and luck play a big role; otherwise, Chaos and the Princes might not leave any chance for victory at the very beginning. As for Hellmar and Vitto, it seems we've discussed this several times in this thread.
Also, the battle between Ory and Leto is interesting. Technically, Leto has the advantage, but I've sometimes managed to win with Ory in this match, even though I don't consider myself a very strong player. Naturally, the black dragons are the key here, and you need to focus all possible physical attacks on them. You should cast Mage's Bane on the witches or hunters at the very beginning and attack with Chaos. Divide the gargoyles into two stacks and either use them to protect the archers and golems or expose them to the enemy stacks. Also, keep in mind that the enemy will use Berserk or Subjugation (usually cast on djinns or mages), so at the beginning, position your troops to protect the mages and golems. You should definitely protect the latter throughout the battle, carefully plan each of their moves, and heal them with Chaos when needed. It wouldn't be bad to attack the black dragons first, removing their retaliation, but again, you need to calculate the attack so that the golems aren't torn to shreds afterward, or you can postpone the attack altogether. Leave the hydras for last, as they are too tough and not that scary with their low initiative. Towards the end, when usually only hydras and golems remain, I create a path of fire and either run around it with the golems, attacking the hydras directly with the hero, or I position them in a corner of the battlefield and wait in the wall of fire if there are two stacks of hydras.
The battle between Vittorio and Nimue is debatable, as again, much depends on Nimue's luck. If she fails to eliminate the defensive stacks at the beginning, by the middle of the battle, Vittorio's powerful ranged attack, combined with Light and Darkness, will shift the advantage to his side.
Against Iris, I don't see a better counter-hero than Deirdra. You can win in this matchup with Deirdra without much skill or effort.
Ibba does a good job against Iris's griffons with her Rune of Invulnerability, berserkers with their retaliation, and the Arkat bears and warriors, which also have a chance to retaliate. But again, eliminating the griffons is only half the battle; against the remaining low-level creatures, Ibba usually lacks something, and the battle usually ends there.
Unfortunately, I don't have the habit of saving replays of difficult battles, which I regret. Nevertheless, I will upload two saves that I have.