[PhilD]

This seems quite expensive, even if it has a good chance of killing multiple commanders - it will only be worthwile if you manage to send in an attack to possibly rout (actually, dissolve) the army once they have no commanders...

But, with Marignon, you have the best asset againt Ermor: excellent priests. Make large Groups of them, with some solid infantry as bodyguards (not necessarily as "guard commanders"), and banish the whole thing away.