Yes, that's exactly what I meant – no losses at all. Hydras are really useful here, and so are the Hunters; if you have a specialist in them, they look good in combination with magic. You definitely need to level up the Trickster; weakening the enemy hero before the battle is essential. As for the undead, it's difficult but possible; you need to focus on initiative and skillfully combine units with combat magic, although unfortunately, it's not always clear how to do this in every situation.