Wow, I don't quite understand how this works. Could you describe the tactics for this battle in a bit more detail, and how many creatures were involved? I think there should have been around 600 creatures, maybe a little less. That's how it was for me, and I defeated them with 33 ranged units – without any losses, but it was a close call, and I used a lot of mana.

The battle with the black dragons went like this: 10 titans were positioned at the top, above the ammunition depot, with 1 archangel underneath, then 1 obsidian gargoyle, then another archangel, and finally three stacks of 1 obsidian gargoyle each at the bottom. The black dragons were arranged in 5 stacks of 89 each, and 1 upper stack with 90. My turn was, of course, first, and the upper archangel flew down and forward a bit. Then, I cast a power field spell covering 3 squares in front of the titans and the ammunition depot, so that only a creature of size 1 could reach the ammunition depot. The second archangel flew forward and down. The black dragons attacked and killed the archangels and obsidian gargoyles, coming under the direct fire of the titans. On the next turn, I cast the expert spell "Haste," and the titans started moving before the black dragons. After that, every other turn, I cast the "Power Shield" spell, positioning it the same way as on the first turn. Additionally, I cast "Haste," "Bless," and "Accuracy" on the titans as needed. As a result, the titans were able to freely shoot down the black dragons, leaving 2-4 creatures in each stack. After there were 4 stacks with 2-4 black dragons each, two archangels were revived with the "Resurrection" spell. After that, the black dragons were finished off. There was a lot of mana with the "Expert Intellect" and "Mana Vortex" skills.
That's how it went. The expert power field is awesome :)