Evolution stone
As soon as Wil stepped inside the courtroom and didn't receive any notification of a no-combat zone, Wil realized that the Imperial palace might be considered as a wild zone.
So, within the palace, he can attack others while he could be harmed in return too.
To test his theory, he unleashed Heavenly Push to blast away the princess despite knowing that he won't be harmed much even if he allowed that attack to hit him.
And the result of his actions made his suspicions become true.
But, then, he remembered how he received EXP buff in the city lord's mansion. So, all he hoped now that he shouldn't receive such buff in this palace so that he gets the perk to assassinate anyone at their rooms while they were asleep, including the king.
Watching his children and his generals blasted away because of the powerful wind, the Dragon King unknowingly took a step back while remembering the scene of the death of six elder dragons.