Maybe some units that are pitifully weak on their own but almost unstoppable in numbers and formation. Kind of an extension of how bowmen work, but with historical precedence. You could have a centurion unit that is weaker and slower than a warrior, but if you get a dozen or so together they can make a phalanx and "turtle" their shields so they can block anything. More to the point, maybe a pikeman who is invulnerable from directly in front but easily dispatched from side or rear (I'm not exactly sure how you would do this--maybe the force field idea, which I still have no idea how it works). The point--literally--is that not even a trow is going to run at a pikeman from the front, not with a bohemian earspoon looking at him. The pikemen would have a very slow turning speed (the weapon being so unbalanced) but fast straight move. The idea would be to have your pikemen get into a square (or circle, though it would be less accurate) so they were defended from every side and could just slowly move across the map, killing anything they found. The opposing strategy would be to send a wight (or a cavalry unit, if you don't want to use the undead) at them, breaking the formation (they would run even more often than warriors do). It should take a very long time to build the formation, since it's all but invulnerable once it's made, and the square should move very slowly (all this achieved by the slow turning speed). These guys would be purely strategic--almost useless against a shade but brilliant versus a wave of thrall or a bunch of knights.
I've also been toying with the idea of a hedge wizard or even a witch unit (not the pointy-hat and warts kind, the historical kind--a middle-aged woman with a knowledge of herbs and so on). This would be a sort of weak sister of the Jman, able to heal minor wounds (maybe half an archer's vitality) but without ammo--I would make this mana-based. No direct attack, but maybe some kind of weak weather power; they can make it snow very hard to obscure your view, or rain on dwarves to put out cocktails. They would obviously cost next to nothing and be very useful in groups.
I've been thinking a lot about "unterunits" lately--weak units that are useful in large groups. I got on this kick after noticing that everyone who did a new wight unit made them nuclear--why? How fun is a game where one wight can kill every player unit on the map? Why not have a weaker wight that runs faster and takes more hits but only does a fraction of the damage? The unit I created (by changing the peasant color table in Amber to give him a green face and hands) I'm calling the revenant. It's supposed to be a kind of wight trainee, not nearly as bloated but with a lot more structural integrity.
