Before he did anything, William ran away from the city gates and dug a deep hole underground, hoping in vain to avoid the senses of anyone much more powerful than him. He asked Atticus to guard him once more, then used his Mana to descend into Reius.
Descending into the World was much more taxing than simply moving things around with his intent. It cost an incredible amount of Mana, nearly emptying William's Mana Reserves of now almost 32 million at a visible pace.
His main body was sitting completely still with absolutely no change to his stance, but something about the light in his eyes had changed, as if he was devoid of all emotion. At the same time, a double of him condensed in the Mortal Realms, promptly using the Seal Element to heavily restrict himself.
His Mana Reserves started filling up again at a slow rate, indicating that his Descent was complete.