Sacred Haven of Debauchery

I just had some fun and, using the training ground, managed to take out two capitals from the map. The hardest part was leveling up the Incubus to a state where its capital guard wouldn't be one-shotted, and then it + the purple demon = a guard turned into cobblestones, being chipped away piece by piece by the whole friendly company.
Bottles and spells for defense would have been very helpful, of course, but unfortunately, I had nothing.
Maybe, instead of the Incubus, it would have been better to take a second purple demon; it would definitely survive the attack, even two, but its chance of petrification is also lower.