A simple example: the opponent has Royal Griffins (or some other unit with infinite counterattack). Using Agony and focusing all attacks on this unit gives us 7 Agony procs in just one turn. Furthermore, when playing as Inferno, you can also apply Berserk, adding +1 proc. What's especially pleasing is that the damage is dealt BEFORE the action is performed, meaning we effectively deal additional damage with Dark magic, and the counterattack weakens with each iteration.
You're talking nonsense. 7 attacks – does your army have no archers at all? Or do the griffins counter the archers?:smile07:
IMO, Agony is useful for development. In a duel – forget about it.