Increased initial creature growth rate.

I have a better idea. You don't necessarily have to carry the Legion statue to the castle; it provides a bonus just by being with the hero. Do the same with all artifacts – they provide their effect to all castles if they are with the hero.

Hmm, that might actually be even better.

And regarding what mrshch wrote, if you do everything as I described, then at the moment when the player places a piece of the Legion in the castle (or rather, not in the castle itself, but in a building of the corresponding level), they will immediately receive the number of creatures that previously just increased on the following week. (the increase also remains).