A simple solution is to use 2 Dark Knights and 1 Alchemist. Have the Alchemist learn Mega-Potion, or have a lot of Potions and Hi-Potions in stock (mixing a Potion and a Hi-Potion makes a Mega-Potion). Have the 2 Dark Knights constantly cast Darkness, and have the Alchemist constantly cast Mega-Potion (one way or the other). That's about it.