In the end, Leon used all the mana liquid stored in all the magic boxes just to keep his replica active. It wasn't because it was like a shadow clone, but it was because the cost of the skill was decreasing by fifteen points with each level up. It made sense since it would be weird if the replica gets stronger than Leon by leveling up. Regardless, at the max level, the replica would drain fifteen thousand mana points per second, but it was better than nothing.
"Just in case, I shouldn't use the mana stored in the soul eaters," Leon nodded to himself. "Although the perfect replica is useful, it won't be helpful against the zombies."
It looks like Leon's worries were unfounded. He didn't feel anything weird when his mind was connected to the perfect replica. Since the copy and the original share the same brain and even the same mana pool, Leon would have noticed if something weird happens.