[Agema]

For this, I'd take the undead, and deploy right at the back. You probably want a reverse communion as per the communion guide. You commune, then your S1 slaves pack out the spellpower which should reduce the Van. This should both inflict plenty of trouble and heavily fatigue your slaves quickly.

With enough masters (probably more than 1 needed), that will eventually push the slaves over 200 fatigue and start killing them, Ideally, the Van army will break, and hopefully the masters' continued casting will kill the slaves by continuing to pummel them with hostile spells as they rout.

If you don't think you'll fatigue out in time, near the end of the cast queue, maybe try a huge BF spell like Will Of The Fates to really push the slave fatigue right up, and then let the AI take over?