Wizard – “Haven” [Campaign 6, Mission 4]

You don't even need to accumulate troops. On the way to Isabel, the Heroes recruit undead (zombies and ghosts) for Zehir. The dwellings are conveniently located along the road. Zehir, with Raise Dead and Phoenix, easily defeats Isabel's army (in my case, she had an Archangel). Therefore, the mission is completed at the beginning of the second week (it happened on day 122 for me).