What about to create a sandbox for training battles between members of an alliance?
It would be great to have an arena where you can battle against your allies to learn about the behavior of heroes, develop new strategies and so on.
Add a way that someone in an alliance can search for a training partner and someone else (or more than one) can accept.
Let us decide whether it’s an autoplay opponent (like PvP) or an live interactive battle.
I know you’ll think about the costs (ingame and for real development) but also think about to keep the game attractive.
About ingame costs… I think 3 worldenergy might be s good price. Alternatively you could use the loot tickets (or something equivalent)