Increased initial creature growth rate.

Therefore, I suggest making it so that artifacts from the Legion set can be stored in the castle. (I don't know how to implement this, but I'm sure it's not that difficult).

There's an even better idea. The Legion statue doesn't necessarily have to be carried to the castle; it provides a bonus simply by being with the hero. Do the same with all artifacts – they provide their effect to all castles if they are with the hero.