Well i have an idea of a diablo 2 desert merc that basically tethers to another existing hero, he will just follow the hero around, able to cast his skills but usually unable to respond to move /AA command
The Cow King from diablo 2, my idea is that if people step on his portals it will summon hell bovines.
Han and Horner is a coop commander yes reimagined as their signature unit in coop mission, the assault galleon with dominion air support by horner.
Too lazy to elaborate further because I am on my phone (on vacation) , i have some ideas on grom and aidan too.