The “An Eye for an Eye” scenario.

When you send Gnomes to the enemy's Inferno, the enemy heroes' armies get stronger with Fire Elementals. I noticed this when I played and exchanged prisoners; Hangwul would arrive at the end of the second month with 120 Fire Elementals, but when I didn't exchange them, he would arrive at the same time with 90-100. Try playing on Veteran difficulty; otherwise, you won't fully appreciate the heroes' abilities. I tried to complete this scenario on Hero difficulty – it's just impossible! Even with runic armor, it's not feasible. I wish I could see the save files of players who completed it on Hero difficulty...