Several units monster units the player can get, like ogres, trolls, darkling warriors and wildlings, that are really fun to see in your own army but don't see much use.
That is because their stats don't scale well with level and they can not use any items, and that feels strange considering everything else gets ever more powerful. It also excludes them from being used in many cases, which is a waste.
I suggest bringing wildlings and darklings into the unit designer as soon as you can produce them, so they can be customized as well; no extra graphics required: just have them use your best spears available so you don't need graphics for other weapons, and the armor pieces need not show on the unit either. Maybe let them have some unique traits to make them special.
As for trolls and ogres, just treat them like henchmen, with the ability to equip any blunt weapon and other equipment you can buy - again, no extra graphics required. I would also love to see them earlier in the tech tree, as they are just too cool to not be used for most of the game - this may require lowering the number of units you can get from an ogre/troll lair.
I suggest this because i believe the effort of implementing this to be relatively small, correct me if i am wrong. It would spice up the battles which usually consist of armies that are pretty uniform in appearance. It would add a unique flavor to the armies at little cost.
Please let me know what you think!