These spells are worth considering:
summon eagle - the landscape is very maze like, but not for eagles
You have an endless amount of time here to build up a force, so do so.
place centaurs on each of the 2 PoPs available.
again, perform the eagle eye tactic,
using an eagle and two dryads.
create another eagle (you'll need him to open the door).
keep creating centaurs until you reach your creature count.
now step off the PoPS, and let the village elder build up a small force.
Then place a centaur back on each.
With full mana, and an army of centaurs, you're now ready for the attack.
the attackAttach form the south. Stand all your free centaurs, and Aurax, at the south door.
send your eagle (not the lord one) to open the door.
Find the button (a building, with a green circular trigger on the floor) and stand your eagle on it.
when the door opens, pause the game
command a single centaur onto each PoP
select all remaining centaurs, and chase after the enemy wizard.
As centaurs die, create more, and carry on sending them after the enemy wizard.
Eventually he'll be killed.
items worth collecting
There is at least a summon knight magic item, and plenty of fear inducing magic items
to collect around the village. Collect these when the battle is over.