For the last level: 4 dwarfs straddle the road at the beginning with a bard to slow. 3 magics go top right with another bard, 4 trolls go between road and water at bottom right. 2 clerics above the trolls, 3 below, 3rd bard in the bottom right corner. Get the bards a level or two quick to cover the entire track w/slow, then get trolls up asap with a couple levels on clerics here and there so they all cover all your trolls. 4 level 4 5-cleric-boosted trolls destroy most things. Upgrades come slow, don't bother upgrading dwarfs til mid-late game, and I didn't upgrade the magics at all until like 2nd to last wave or so (weak vs phys).