Let's say I am playing Cao Cao, and I want to help Yuan Shao fight against Dong Zuo at his boarder, by sending Xiahou Dun with 4 units under him. So I park Xiahou Dun's unit right next to Yuan Shao's stack. Alone, Dun is pretty vulnerable, but next to Shao's stack he is protected. The way this would work in Warhammer is that on Yuan Shao's turn he would end up moving to some location I do not expect and possibly leave Dun completely exposed to getting wiped out by Dong Zuo, because i cannot match Shao's move until my turn.
So the request is: Let me attach Dun's unit to Shao's stack, and as soon as that stack does any movement at all, I get to do Dun's movement on Shao's turn, not my turn. He is effectively under Shao's borrowed command. So if Shao does a move to attack, before he actually attacks, I have the option to move to him and reinforce., etc.
You could put limitations on this to curb abuse like:
- In this state you cannot initiate an attack
- Cannot be a full stack, just a support stack.