Inferno tactics.

Yes, during a siege, you can wait for the devils so they aren't killed immediately. I agree that it's difficult for the Castle faction to defend against the Inferno, but letting the Imps act as cannon fodder and turning them into Pit Fiends or preserving them to steal mana is a good strategy. Use the Magogs to provide cover, and gather a group in the passage so that the Magogs can attack multiple units, and the Cerberi can help take out the Monks. Devils are better at taking out Monks because there are fewer of them, and even though they only attack once, they have much higher hit points and damage than archers, which always compensates for the difference in numbers between archers and Monks. I don't think anyone will rush the archers with Devils, unless they're suicidal. And you can wait for the Efreet if only the Cruisers and archers remain in the enemy camp; the Efreet will definitely take out the Monks, and the Devil, for example, can take out the Cruisers, thus preventing them from using ranged attacks, and allowing all the Magogs to survive longer. (IMHO, it's a bad tactic, but who knows:))