Now we're getting into the spirit of it! I like the last suggestion. But we don't need any more external destruction. We've already done that. Now it's just self destruction. It fits the nature of this VC (it's all a death wish anyway) and it provides the gameplay value of wrapping up the game. Actually, the mana used should be equal to the xp of the caster. That number is basically equal to the mana that they have ever used. So in effect we have one spell that doubles the damage ever done by an individual, in one instant. If you are playing smartly, then maybe you reach this tech right when you have 4 Liches with enough accumulated xp to finish the game right then. Or maybe you need to burn down a few holdout cities (on distant islands) with Consume Souls first. When you are ready, all remaining spellcasters learn this and cast it together... game over.