The dungeon of Ruyang Mansion did have tight defenses!
It would be a very difficult quest for a person to invade the dungeon and free the prisoners without alerting anyone. Zhang Wuji and Zhou Zhiruo's appearance helped Happy quite a lot.
The Eighth Prince's capture and the appearance of two elites from the world of martial artists shocked the guards of the royal mansion into action, and most of them were afraid for their master. They quickly headed to the entrance of the mansion, which was why the originally tightly defended royal mansion had many holes in its defenses.
With practically no effort and with very little time wasted, Happy brought two men with cold expressions and who were dressed in night traveling clothes near the dungeon.
The people behind him were famous Beijing fighters Iron Saber and Thick Sword. They were solo players who became famous by challenging the powerful players on Dragon Rank in Beijing.