Evro
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Yesterday, I completed this mission on my second attempt. The mission is quite simple. The maximum losses, if you don't use the banishment spell, were with Zephyr.
The minimum losses were with Raelag; the black dragons are incredibly effective, you can practically play with your eyes closed. Findan cloned the emerald dragons, and the clone was a huge help throughout the game. Godric with his archers was just standing around doing nothing; the archers did all the work themselves.
Overall, thanks to all the forum members for the tips and to the developers for creating such an amazing game; I've completely immersed myself in the world of Heroes.