Ever watched dwan of the dead? making an armageddon spell based on that would be really cool, start with one 'dead' unit, every unit he kills turns into another 'dead' unit, etc. even if a 'dead' unit loses in combat, it would pass on a promotion of some sort (doomed or cursed or infected) so that when it dies, it will become 'dead'. Perhaps when they raze a city, a certain number of 'dead' units will spawn depending on the population. Of course, you'll likelly have little idea what I'm talking about if you haven't seen dawn of the dead (2004 remake). But it'd make such a cool armagedon!