Your most powerful hero is the one whom your friends can use. And adding a friend, you can use his most powerful friend as well.
A player can use only the most powerful hero of the friend, no one can choose the hero to share.
If your most powerful hero changes - it replaces in the list automatically.
Important: You can not use 2 similar heroes simultaneously.
When you take a hero of your friend in a battle, it replaces your similar hero from the squad automatically.