Why did the Monkey King in The Journey to the West suddenly appear in the Dragon Palace in Weihe River?

That's just the Monkey King's invisibility. The Monkey King somersaulted to the Dragon Palace in Weihe River, then sneaked into the banquet of the Dragon King and suddenly appeared, so there was a scene in which the Monkey King suddenly appeared in the Dragon Palace in Weihe River. That chapter is about the Monkey King being stopped by King Jinghe and the Monkey King going to hell to find out the truth.

When the Monkey King arrived in the underworld, he discovered Qin and learned that the Dragon King of Weihe River and Wu Dexing had bribed. Then the Monkey King sneaked to Wu Dexing's house. As soon as he heard that Wu Dexing was not at home, he turned into Wu Dexing to cheat his wife. Wu Dexing's wife didn't expect her husband to be fake, so the Monkey King found out the evidence that Wu Dexing framed King Jinghe.

Then the Monkey King left Wu Dexing's home under an excuse, and flew to the Dragon Palace in Weihe River with a somersault. In Why the Dragon Palace, the Monkey King saw Wu Dexing drinking with the dragon king of Weihe River, and they were still laughing at the Monkey King's incompetence. The Monkey King bypassed the Dragon Palace guards through invisibility, and was standing at the wine table of two people, listening clearly. In desperation, the Monkey King appeared on the spot. But at this time, there is something wrong with the Monkey King's appearance. He is standing behind Wu Dexing, so Wu Dexing is speaking ill of the Monkey King. The Monkey King has stood behind him. The Dragon King of Weihe River, sitting opposite Wu Dexing Jun, clearly saw the Monkey King suddenly appear behind Wu Dexing Jun, and was too scared to speak on the spot.

Wu Dexing thought the dragon king of Weihe River was drunk and made fun of him for not drinking enough. After being teased by Wu Dexing, the Dragon King of Weihe River quickly woke up, and then there was a big war between the two sides. They were naturally no match for the Monkey King, and were finally caught in heaven and put in prison. On the whole, did the Monkey King use somersault cloud and invisibility? Suddenly appeared in the Weihe Dragon Palace? Yes